There's been a lot of complaining about how this film didn't up the ante on the first one, and about how there wasn't enough action, and I can't help but wonder what the hell these people are blabbing on about. The film I saw was badass from start to end, with just the right balance between action and character development, and the same perfect tone that I loved in Iron Man 1. While there are a ton of characters and events, it all fits perfectly together and builds up really nicely to the Avengers movie, while also giving Stark his "dark period" and organically introducing War Machine and Black Widow. While this didn't revolutionize the superhero genre or delve deeply into complex philosophical themes, it was basically the perfect badass comic book movie. If you wanted more action, go watch xXx or something, you psycho.
In a sentence:
Continuation of the awesomeness of Iron Man 1, upping the ante on the comic book references, action and character development so as to build up nicely to The Avengers. Can't wait for the rest of the Marvel flicks.