Alright, how is there not a topic on this yet? I've watched it twice in as many days; I find it a fantastic film on its own, but what amazes me more is Marvel's concept of having multiple storylines that all culminate together in a single movie like this. This naturally is exactly what comic book crossovers are, but I'd love if more franchises tried it.
As far as the movie itself, it's the perfect blend of action and hilarious entertainment. My only hopes were that it would be like the Ultimate Avengers animated movie but better, and it played out in spades. The climactic action sequence had incredible cinematography, and the dialog in between fights was perfectly timed and spot-on.
Well played, Mr. Whedon.