By perfecting the comic book superhero formula and creating the first big-budget shared universe with The Avengers in 2012, Joss Whedon and Marvel Studios came to define this decade of blockbuster filmmaking.
In Marvel's comics, narrative closure is always deferred, every ending a new beginning. Iron Man 3, with its now world weary characters and aging actors, draws attention to how live action is different from comics.
One of the biggest issues a comic book movie adaptation has to overcome is staying/not staying "true" to the source. However, when there are multiple configurations of same, such creative reverence becomes harder and harder.