It wasn't too shabby, but it didn't do a lot for me.
There's an established pattern for the successful comic book franchises, which has stayed consistent since Christoper Reeve's time with Superman. The first movie is good, possibly great. The second movie is even better -- bigger budget, no origin story, and increased skill and confidence from the director, cast, and crew. Then, a few years later, everything starts to go wrong with the third movie. Each franchise has stumbled for different reasons, but there's been one constant for all of them: the second sequel introduces too many new characters and subplots, with no real idea how to tie all these elements together into a cohesive, enjoyable story.
Comparing Iron Man 2 to previous superhero films, it does just about everything the first sequel does right and just about everything the second sequel does wrong. It's probably better than Spider-Man 3, the best of "3's", but it's got nothing on Spider-Man 2, X-Men 2, and The Dark Knight.