[**Spoilers for Buffy The Vampire Slayer (1996-2003), Astonishing X-Men (2004-2013), The Avengers (2012), Agents Of S.H.I.E.L.D. (2013 to Present), and other works by Joss Whedon.]
Joss Whedon has, in many ways, literally written the same story with each property he has worked on. Yes, there are some differences, but if you have seen a single work of his, you will see the same elements each time. All of these story elements are found in our focus point, the television show Buffy The Vampire Slayer.
The first story element involves heroes unintentionally aiding a villain’s master plan by not doing enough. In the case of Buffy The Vampire Slayer, we see this most prominently during Season One when Angel is too cryptic and the rest of the leads are too reluctant. Meaning if Buffy and the rest of her original group were more proactive, The Master (Season One’s villain) would have been defeated without releasing him. To prove my first point, I give you the team in The Avengers hanging around the Helicarrier waiting for Loki to talk instead of looking for his mind-controlled minions.
The next story element is having a female lead as the center point of a story or series. Now this is definitely not a bad thing, but it has become somewhat predictable of his style. From Buffy to Skye/Daisy Johnson/Quake (Agents Of S.H.I.E.L.D.), he usually has a female lead as the protagonist. Case in point is Kitty Pryde during he and John Cassady’s run on Astonishing X-Men. She is essentially the lead character for readers to relate to via her thoughts (Astonishing X-Men, Volume 1: Gifted ).
Lastly, there is also a common story element involving poor communication between characters. In Buffy we see this happen a lot with characters not communicating about ways to resolve internal issues in the group (Ex. Season 4 episode 20 “The Yoko Factor” ). The movie Toy Story (1995), which Whedon co-wrote, shows signs of this when the toy characters act without discussing things.
In conclusion, I believe that without creative collaboration, Joss Whedon would probably not have generated as many successful products as he helped create given the similarities between them.