The moment you have a main character whose job it is to run around stopping things from happening, you have a reactive protagonist, which means a weaker narrative. When you have a weaker narrative, you end up throwing all kinds of nonsense at the screen, hoping that no one will notice that you have a reactive protagonist. This is, incidentally, why Batman rarely shows up in Christopher Nolan’s Batman movies — Nolan understood that the protagonist of his Batman movies had to be Bruce Wayne, not Batman, and that, for his narratives to succeed, the bad guys had to be reacting to the actions of Bruce Wayne, not Batman reacting to the actions of the bad guys.

Todd Alcott with a terrific analysis of the Avengers movie screenplay.

He has also been writing a multi-part take on The Dark Knight Rises screenplay over at his blog.