For fans of big summer action flicks, this is a very good example of the sub-genre "Super Hero". The action is well choreographed and exciting, with New York City, as usual, given a hard time.
(Poor NYC and poor Tokyo too, what with that Godzilla constantly.)
But, as a fan of Joss Whedon's work, it was the banter and bickering between the ill-assorted heroes of the Avengers that I really enjoyed. That and the Hulk! Frankly, I had never understood the appeal of the Hulk in the comics, but in this film he's one of the best characters... and when he goes Green, he's either really impressive in his rage or wonderfully comic. (Hulk one-on-one with the villain Loki - watch for it.)
There's a lot of character based humor in this film; it's clear that the director and screenwriter both (Joss? both of 'em?) understand(s) the different points of view of his very different heroes. i'd love to watch a poker game between these guys.
Screen capture from The Avengers from Collider.com, more pic there.
A fun summer movie with much much better dialogue than usual.