It truly is a fantastic superhero film. There was -- if I have ANY complaint -- maybe just a pinch too much outright humor (some of the dialogue was very Whedon-ish, and less Avengers-ish, at times)...but as complaints go, "it was too awesome" is kind of a weird one.
All in all it was just great. Every character got a chance to shine, every character was handled respectfully, every character did stuff, every character got in some good lines and some solid acting. Black Widow knocked it outta the park (instead of just being some T&A, like was expected), this was my favorite Hulk/Banner yet, and all the returning badasses -- Cap, Iron Man, Thor -- were spot-on. Even my boy Hawkeye got to look badass and fill an appropriate role.
Good stuff all around. Just really, really, good stuff.