I just got back as well. Epic. Totally epic. Lived up to the hype. Not going to give a detailed review, I just want to gush a little. Every character had their moments and the dialogue was sharp (thank you Whedon). One of the complaints I have about the other Marvel films is that the action feels lacking towards the climax, but in Avengers it never lets up. I was very sad when it ended and I can't wait to see it again.
There was a moment when I was just sat in the cinema thinking 'I'm watching Captain America, Iron Man, Bruce Banner and Thor arguing. Holy shit'.