I haven't seen Thor yet, though I heard it was a decent/good film, but I though the first Iron Man film was the best recent comic book film until the Dark Knight came out, and not because I think its the definite comic book film, but rather one that suits the character very well. I still think the best may be Spider-Man 2 because it has that perfect mix of action/story/emotion/romance that really makes it stand out. And if SM3 wasn't such a disappointment amongst fans, then I think that that would've been the franchise that everyone would try to measure things up to.
But I think ever since superhero movies started becoming popular after the success of X-Men and Spider-Man in the early 2000s, there seemed to be more focus on just getting a movie out rather than getting a good movie out. But like I said, Marvel is ambitious and I like that, and there's no doubt that Cap and the Avengers will make their share of money, but like TIH said, its easier to back up something like Batman that has proven to be successful than it is to back up the Avengers because there's that slight chance of the project being rushed out to accommodate all of the different stars and trying to find a way to fit each of them in the right way. Kinda like how people hated the treatment of some of the more major X-Men characters in the trilogy where it seemed more like Wolverine was the only star with a supporting cast around him.
TDKR could easily fail like SM3 did, but since it doesn't seem like Nolan has the studio changing his ideas around and forcing him to include or exclude certain characters, I feel a lot more confident that his vision will both do the character justice and create a riveting story.