For the last four years, "Agents of S.H.I.E.L.D." has delivered outstanding superhero television. Each week, a diverse and talented cast solves problems within the Marvel Universe. When "Agents of S.H.I.E.L.D." first began, it was spun-off from Marvel's highest earning film, "The Avengers." That film was the coming out party for heroes like The Hulk, Black Widow, Hawkeye, Captain America, Thor and Iron Man. In a way, "Agents of S.H.I.E.L.D." set out to solve the mysteries that the Avengers left in their wake. The existence of enhanced people, alien tech, and even greater global threats.

RELATED: Legion: 15 Reasons It's The Best Superhero TV Show

"Agents of S.H.I.E.L.D." was really the first show to get the cinematic spin-off treatment, which is what makes this show so special. That connected-ness, along with the show's commitment to showcase heroes and villains from Marvel comics, along with a healthy team -- a family -- of S.H.I.E.L.D. agents who protect and fight for one another, clearly makes this the best superhero show on television. Let's countdown some specific examples.

WARNING: The following list contains spoilers for Marvel's "Agents of S.H.I.E.L.D."

15 AGENT CARTER CONNECTIONS

Agent Carter Shield

“Agents of S.H.I.E.L.D.” takes place in modern times, but the show always pays tribute to one of S.H.I.E.L.D.’s most famous founders Peggy Carter. The clearest example of this is the show’s regular reminder to the audience that S.H.I.E.L.D. used to be the S.S.R., the Strategic Scientific Reserve. Whether Coulson is giving a base tour to government officials or polishing the S.S.R. memorabilia in his office, he always recognizes S.H.I.E.L.D.’s history with Peggy.

In Season 2, the show uniquely connected to Peggy and the Howling Commandos when they guest-starred in the season opener. Peggy and the Commandos arrested season villain Daniel Whitehall, who had been a follower of the Red Skull and Hydra. That scene featured the S.S.R. acquisition of many unknown artifacts, including the Kree alien (whose blood saved Coulson and Skye’s life in Season 1) and the Terrigen Crystal obelisk that would later transform Syke into the Inhuman Quake. Hayley Atwell guest-starred on the show again in Season 2, to interrogate Whitehall about his unnatural long life. This connected to Skye’s mother, Jiaying, which made Peggy an important part of the season. Since “Agents of S.H.I.E.L.D.” was the first Marvel Television spin-off, you could say that the success of the show helped greenlight “Agent Carter,” which was the best way to pay tribute to a founder of S.H.I.E.L.D.

14 STATE-OF-THE-ART-TECHNOLOGY

Lola Shield

Another fearless founder of S.H.I.E.L.D is Howard Stark, the father of Iron Man himself Tony Stark. Howard’s knack for innovation can be seen all over “Agents of S.H.I.E.L.D.” through their high-tech gadgets, cars, and planes. Coulson’s flying red convertible, Lola, was first seen as a prototype designed by Howard Stark at the Stark Expo in “ Captain America The First Avenger.” Coulson is clearly a Stark fanboy if he was able to procure one of Howard’s flying cars.

“Agents of S.H.I.E.L.D.’s” main sources of transportation are clearly the most high-tech of any television show. Coulson’s plane in Season 1 (which was known as the 616 Bus), the cloak-enabled S.H.I.E.L.D. Quinjets and the helicarrier-like Zephyr 1 are all planes that outshine other superhero shows by a mile. Then there are the hands-on tech pieces, like the non-lethal “night-night” guns Fitz designed. Coulson himself was brought back to life by the T.A.H.I.T.I. project, which employed a blend of Earth science and alien technology. When he lost his hand in Season 2, Fitz built him a new one, complete with a digital version of Captain America’s shield.When Skye’s body was being destroyed by her own powers, Simmons designed resonance-dampening gauntlets to protect her from tremor vibrations. Even Doctor Radcliffe’s Life Model Decoys and Matrix-esque Framework outpace the tech on other superhero shows.

13 INCREDIBLE VISUAL EFFECTS

Inhumans Shield

From the cloaking technology of the Quinjet to the powerful shockwaves from Quake’s gauntlets, the VFX team at “Agents of S.H.I.E.L.D.” is never afraid to push the envelope when they translate something from comic book page to television screen.

In Season 1, the VFX team illustrated the powers and dangers of Project Centipede and the Deathlok program. This included the highly volatile nature of the Centipede serum as well as the fully weaponized Deathlok suit. In Season 2, the VFX team powerfully animated Daisy Johnson’s terrigenesis transformation. When Triplett, Skye, and Flowers were exposed to the terrigenesis gas, they were encased inside black cocoons. When Skye emerged from the cocoon, the effects were absolutely incredible. During Season 3, the effects team got to showcase the vast powers of Inhumans like Yo-Yo, Joey, Lincoln, Lash, and Hellfire. Hive’s transformation from Grant Ward into a tentacled squid-like beast was insane and totally movie quality. Season 4 kicked off with some of the best VFX yet, by revealing the flaming skull of the Ghost Rider and his terrifying Hell Charger.

12 DIVERSE CASTING

Agents of SHIELD

"Agents of S.H.I.E.L.D." is the best superhero show on television because of its amazing cast. Each actor brings such depth, such emotion, and such intensity to his or her role. The casting is strengthened by its unmatched diversity. While most superhero shows feature one or two men or women from different ethnic or national backgrounds, "Agents of S.H.I.E.L.D." continuously casts men and women of different ages, skin tones, and nationalities.

For instance, Clark Gregg is a Caucasian-American man who is well into his 50’s. Coulson is both super dad and super spy, and that’s not a role a 20-year-old could play. Ming-Na Wen is Chinese American, also in her 50’s. She could have been typecast as someone's mother, instead “Agents of S.H.I.E.L.D.” booked her as “The Cavalry,” the most feared woman in all of S.H.I.E.L.D. Chloe Bennet is also Chinese American and is in her 20s. Elizabeth Henstridge and Iain de Caestecker are both 29 and are both citizens of the United Kingdom. Henry Simmons is in his 40s and is African-American. Natalia Cordova-Buckley is a Mexican actress in her 30s. The diversity in age, ethnicity, and nationality sets this show apart from every other superhero show on television.

11 DIVERSE SHOWRUNNERS

Jed Maurissa Shield

Much of the diversity in casting can be attributed to the intentions of both showrunners Jed Whedon and Maurissa Tancharoen. They are a mixed-race couple who don't shy away from diverse casting or even mixed-race romantic pairings on the show.

They have paired up Melinda May and Grant Ward, Skye and Grant Ward, and Mack and Yo-Yo -- all mixed race couples. Not only is it rare to see diverse relationships on superhero shows, it’s also rare for superhero shows to be run by a woman of color. “Lucifer,” “Legion,” and “Gotham” are all run by men. “Arrow,” “Legends of Tomorrow,” and “The Flash” are all executive produced by a woman, but she doesn’t serve as showrunner on any of those shows. "Supergirl” and "Jessica Jones" are the only shows with female showrunners -- but Marissa stands alone as a showrunner who also comes from an Asian background. When diversity is usually represented at the executive level like this, it does affect the casting on a show, and in “Agents of S.H.I.E.L.D.'s" case, it has afforded women like Wen, Bennet and others an opportunity to shine.

10 STRONG FEMALE CHARACTERS

May Daisy Shield

“Agents of S.H.I.E.L.D.” also boasts more female characters than “Arrow,” “Gotham,” “The Flash,” “Luke Cage,” “Daredevil,” “Legion” and “Supergirl.” None of the women on “Agents of S.H.I.E.L.D.” are lawyers or news reporters or mental patients (like on other shows), they are S.H.I.E.L.D. agents. They are pilots, military tacticians, biochemists and superheroes.

These women stand in the ranks alongside Maria Hill, Natasha Romanoff and Peggy Carter. Even the show’s supporting female characters are strong, intelligent women. Supporting roles like the mysterious “woman in the flower dress,” played by Academy Award nominee Ruth Negga, Bobbi “Mockingbird” Morse, who is both a biochemist and super soldier. Senator Nadeer, Agent 33, Victoria Hand and even Skye’s mother, Jiaying, are all powerful, diverse, well-developed female characters. Not one of these women was brought onto the show to be someone’s love interest. They all have their own storylines, motivations and desires. This also applies to Natalia Cordova-Buckley, whose character Elena “Yo-Yo” Rodriguez was such a compelling character that she even got her own digital spin-off titled “ Slingshot.” These women are strong, intelligent, kind and consistantly work together for what's right.

9 FITZSIMMONS

Fitzsimmons Shield

No superhero show would be complete without a brilliant tech support team. On "Agents of S.H.I.E.L.D." Jemma Simmons and Leopold Fitz provide that support as the dynamic duo “FitzSimmons.”

Their teamwork and friendship over the last four seasons has blossomed into a remarkable romance. They have been through thick and thin together: When Jemma was infected by the Chitauri helmet in Season 1, Fitz exposed himself to the infection to come up with the vaccine to save her. In Season 2, Jemma and Fitz’s relationship was painfully strained because of Fitz’s brain damage. In Season 3, when Jemma vanished into the Monolith and was sent to the exile planet Maveth, Fitz moved heaven and earth to find her and rescue her. Their friendship, their love for one another, their constant belief in one another is a powerful reminder that love can endure, even in the midst of harrowing conditions, like Hive, Hydra, and LMD takeovers. Their love on “Agents of S.H.I.E.L.D.” is completely unmatched by any other superhero show that’s currently on television.

8 HEALTHY TEAM DYNAMICS

Mack Daisy Shield

“Agents of S.H.I.E.L.D.” is different from other shows because it's not about one hero -- it's about agents -- plural. Shows like “Legion,” “Daredevil,” “Jessica Jones” and “Luke Cage” all focus on the growth, struggle and accomplishments of one hero. Sometimes those heroes are supported by teams, like on “Supergirl, “The Flash,” and “Arrow,” but those shows are still about one lead person.

While the “Agents of S.H.I.E.L.D.” team has dealt with various moments of betrayal within their own ranks, they have always bounced back. They also have a compelling family dynamic. For instance, May is like a surrogate mother to Daisy and has taken Daisy under her wing countless times. Coulson is a surrogate father figure to all the members of the team, especially Daisy. Mack is a big brother to everyone, always ready to defend the members of his team in a firefight. Even in the midst of great heartache and even greater loss, these characters always work through their issues, always forgive each other, and always choose to believe in one another, despite great odds.

7 COMPELLING VILLAINS

Grant Ward Shield

The dynamics of the team are only as good as the villains that provoke them, and "Agents of S.H.I.E.L.D." has some of the best villains superhero TV has to offer.

The Season 1 villain was John Garrett, who ruthlessly betrayed S.H.I.E.L.D. to prolong his own life via the Deathlok program. In Season 2, Daniel Whitehall assumed the responsibility of Hydra and used S.H.I.E.L.D. to track down the Terrigen obelisk. That led S.H.I.E.L.D. to Skye’s mother, Jiaying, who turned on S.H.I.E.L.D. and her daughter to save her own people. Gideon Malick rose from the ashes of Hydra in Season 3 to reveal the cult of all cults -- the true reason Hydra was formed: to worship and restore Hive to planet Earth. All of these villains were served by the indestructible Grant Ward. He served these villains and then offered his body to become the greatest Hydra sacrifice of all time. When Hive possessed Ward, he bent Daisy to his will, which turned her against S.H.I.E.L.D. and tore apart her team. Now Ward is back, thanks to Aida and the Framework, and the greatest villain of all will be the “what ifs” the team will face when the show returns in April.

6 HAIL HYDRA

Hydra Shield

During Season 1, "Agents of S.H.I.E.L.D." had the impossible task of keeping Marvel’s biggest secret: that Hydra would be returning in “Captain America: Winter Soldier.”

As S.H.I.E.L.D. was falling inside the larger Marvel Cinematic Universe, Hydra was rising. Hydra claimed the life of Director Nick Fury (officially, anyway), which forced Fury to pass the Director title to Coulson. S.H.I.E.L.D. then went into the shadows, as Hydra amassed loyal followers. Over the course of four seasons, Hydra’s true purpose was revealed. The writers on "Agents of S.H.I.E.L.D." created a backstory for Hydra that spanned not only centuries, but also galaxies. Hydra’s entire purpose was to serve the death-bringing Hive. Their logo was even echoed in the design of Hive’s face. Hydra has been S.H.I.E.L.D.'s greatest foe and will continue to be, even in the upcoming alternate reality of the Framework. Considering S.H.I.E.L.D. and Hydra’s decades-long battle in the comics, it makes sense that no matter which villains rise each season, Hydra will always be there lurking in the shadows.

5 MARVEL COMIC BOOK CONNECTIONS

Ghostrider Shield

One of "Agents of S.H.I.E.L.D." greatest strengths is how it creatively connects to the source material of Marvel comics. Each comic book-based hero and villain has been incorporated into the show so creatively, so seamlessly, a task not every superhero show gets right.

In Season 1, Mike Peterson became Deathlok. Deathlok was first introduced in 1974 in “Astonishing Tales” #25. He was an enhanced cybernetic super soldier created by Rich Buckler and Doug Moench. In Season 2, "Agents of S.H.I.E.L.D." introduced Inhumans and revealed Skye’s true identity to be Daisy “Quake” Johnson. In the comics, Daisy Johnson was first introduced in 2004 in “Secret War” #2. She was created by Brian Michael Bendis and Gabriel Dell’Otto to be a powerful Inhuman with seismic abilities. In Season 3, "Agents of S.H.I.E.L.D." brought its Hydra storyline to a head (pun intended) by introducing HIVE. In the comics, HIVE was a genetically engineered parasite created by Hydra to represent their figurehead. His character was created by Jonathan Hickman, Brian Michael Bendis, and Stefono Casselli in “Secret Warriors” #2 in 2009. In Season 4, "Agents of S.H.I.E.L.D." introduced Holden Radcliffe and his Life Model Decoy Project. Radcliffe was created by Marc Sumerak and Mike Hawthorne in 2005’s “Machine Teen” #1. Season 4 also introduced the Ghost Rider Robbie Reyes. Felipe Smith and Tradd Moore created this new version of Ghost Rider for “All-New Ghost Rider” #1 in 2014.

4 MARVEL FILM CONTINUITY

Steve Rogers looking at a SHIELD logo in Captain America: The Winter Soldier.

While other superhero TV shows like “Arrow,” “The Flash,” and “Supergirl” crossover with each other, "Agents of S.H.I.E.L.D." crosses over with the films like “The Avengers,” “Thor: The Dark World,” “Avengers: Age of Ultron,” and “Doctor Strange.”

The best example of this comes from “S.H.I.E.L.D.’s” two-part episode in Season 1 that connected with “Captain America: The Winter Soldier.” While fans watched the episode “Turn, Turn, Turn” on Tuesday, April 8th, 2014 -- the episode that aired just days after “Winter Soldier” opened in theaters -- they were suddenly faced with the truth: that S.H.I.E.L.D. had been completely compromised by Hydra. This was a bomb that obliterated "Agents of S.H.I.E.L.D." in the best way possible. The show was never the same after “Winter Soldier,” which was a fascinating challenge that the show handled brilliantly. In Season 2, Coulson resurrected a helicarrier to help the Avengers rescue the citizens of Sokovia in “Avengers: Age of Ultron.” In Season 3, Coulson mourned over the death of Peggy Carter -- her funeral was seen in “Captain America: Civil War.” In Season 4, AIDA used the Darkhold to open a portal to another dimension, which looked exactly like the portals Stephen Strange and the Ancient One were opening in “Doctor Strange.”

3 MCU GUEST STARS

Lady Sif Shield

Connecting with the MCU films also means featuring some amazing MCU guest stars.

Samuel L. Jackson has appeared on the show twice as Nick Fury-- first to valiantly rescue agents Fitz and Simmons from a watery grave and secondly to hand Coulson the literal “Toolbox” to rebuild S.H.I.E.L.D.. Maximiliano Hernández's Jasper Sitwell also appeared on the show three different times during Season 1. Jaimie Alexander's Lady Sif has also appeared in Season 1 to track down the Asgardian sorcerer Lorelei and in Season 2 to track down a rogue Kree warrior who had erased her memory. Hayley Atwell guest starred as Peggy Carter twice in Season 2, first to recover the obelisk in 1945 and then to interrogate Daniel Whitehall about his ties to Hydra. Cobie Smulders' character, Maria Hill, also appeared in the "Agents of S.H.I.E.L.D." pilot and the various episodes in Seasons 1 and 2. After making a brief appearance on the World Security Council in “The Avengers,” Powers Boothe joined the cast of "Agents of S.H.I.E.L.D." as Gideo Malick in a recurring guest-starring role in Season 3. Stan “the Man” Lee even made a cameo in the Season 1 episode “T.R.A.C.K.S.”

2 THE WHEDONVERSE LIVES ON

Whedonverse Shield

Another reason "Agents of S.H.I.E.L.D." is the best superhero show on television is because it is a “Whedonverse” show. The show is executive produced by three Whedons: Joss, Jed, and Maurissa. The show was conceptualized by Joss Whedon after the death of Phil Coulson in “The Avengers.” Joss then brought on Jed and Maurissa, whom he had worked with previously on “Dollhouse” and “ Doctor Horrible’s Sing-Along Blog”.

Since Season 1, "Agents of S.H.I.E.L.D." has cast Whedonverse actors. For instance, Clark Gregg appeared in “Much Ado About Nothing,” which was written and directed by Joss Whedon and co-starred both Jed and Maurissa. J August Richards, who plays Deathlok, previously worked on Joss’ “Buffy the Vampire Slayer” spin-off “Angel.” Amy Acker, who played Coulson’s cello-playing love interest, also worked on three Whedon projects: “Dollhouse,” “Angel,” and “Much Ado About Nothing.” Reed Diamond, who played Hydra agent Daniel Whitehall, also co-starred in “Dollhouse” and “Much Ado About Nothing.” Dichen Lachman, who played Skye’s mother Jiaying was a main character in “Dollhouse;” she played Sierra. Patton Oswalt, who plays multiple Koenig brothers on “S.H.I.E.L.D.” previously appeared on “Dollhouse.” Lastly, the late Ron Glass, best known for his role as Shepherd Book on “Firefly,” played Coulson’s T.A.H.I.T.I. doctor.

1 COULSON LIVES

Coulson Shield

Finally, the number one reason that "Agents of S.H.I.E.L.D." is the best superhero show on television is because the show resurrected Phil Coulson.

Due to his wonderful appearances in “Iron Man,” “Iron Man 2,” “Thor,” and “The Avengers,” Coulson was the glue holding the Marvel Cinematic Universe together. Coulson’s death catalyzed The Avengers to put aside their differences and win the Battle of New York. His death came as such a shock to fans that they started the hashtag campaign #CoulsonLives.

Joss Whedon was so inspired by this outpouring of love from the fans that he pitched a show starring Phil Coulson to ABC. Phil Coulson's miraculous resurrection on "Agents of S.H.I.E.L.D." was the main focus of Season 1. Throughout the series, Phil has become a surrogate father to Daisy, to Mack, to Bobbi, to Hunter, even to Fitz and Simmons. His optimism, his commitment to do what's right and his passion for his team makes him a remarkable hero, despite not having powers. One of the best moments on the show was when Nick Fury handed Coulson the keys to S.H.I.E.L.D.'s kingdom and made him Director. Coulson's journey on this series has been remarkable -- he truly makes "Agents of S.H.I.E.L.D." the best show on television.

Do you think "Agents of S.H.I.E.L.D." is the best superhero show on television? Let us know in the comments!