OK, I guess it falls to me to (sort of) run counter to the otherwise glowing praise:
I enjoyed the movie, and thought it was fun and funny, but I don't think it measured up to its potential, in that the story felt paper thin. I mean, even in a comic book movie, you ideally want to have some kind of substantive character arc for the protagonist or protagonists. Even looking at, say, last year's Thor movie....that movie had a pretty clear character arc for Thor. It was meaningful to talk about where the character was at the beginning vs. at the end.
In The Avengers, what are the character arcs? Stark learns that there's a benefit to working with others? Captain America learns how to deal with the modern world? That's extremely thin stuff. It seemed like they were going somewhere with Banner's efforts to keep the Hulk contained, but that amounted to nothing in the end. And, surprisingly, the story thread dealing with Thor's relationship to Loki was completely wasted.
Don't get me wrong. I thought the movie had great Whedonesque dialog. But it still seems like there were some pretty big wasted opportunities here.