There are very few good comic book movies. The Avengers is one of them. That's why it's appropriate that Joss Whedon - writer and director of the film - was asked at the movie's press day how to make a good comic book adaptation. His answer, while seemingly obvious, should be heard by both Hollywood and the fans:
It's capturing the essence of the comic and being true to what's wonderful about it, while remembering that it's a movie and not a comic. I think Spider-Man, the first one particularly, really captured [the spirit of the comic]. They figured out the formula of oh, tell the story that they told in the comic. It was compelling, that's why it's iconic, but at the same time they did certain things that only a movie can do [but] were in the vein of the comic.
I think you see things like The League of Extraordinary Gentlemen, where they just threw out the comic, or Watchmen, where they do it frame for frame, and neither of them work. You have to give the spirit of the thing and then step away from that, and create something cinematic and new.
It's so simple. You've optioned the comic (hopefully) because it works, because it's good. Don't fuck with what's already good. But don't then be so beholden - as some fans might want you to be - to every single piece of the lore. Throw things out or reshape things as needed to make a movie that serves the best parts of the comic you're adapting.