The movie was a lot of fun to watch, but it suffered an extreme case of "middle movie syndrome" (like Bob said, it was setting up it's own sequel, Thor, Cap, Avengers, possibly some other movies), and lacked the kind of focus that the first movie had. In a lot of ways, it was very much like a comic book, and that was both good and bad. The colorful aesthetic, interesting characters, multiple subplots, it helped to make it more than I expected it to be, but it also crowded out Tony's story, and insured the incredibly awesome Whiplash got hardly any screentime. Again, not bad, but it was too busy playing rehearsal for everything else.
Oh, and one nitpicky thing that got on my nerves: did Bill O'Reilly really have to be in this movie? Was it necessary to include anyone from that wretched hive of scum and villainy that is Fox News? At all? I get that it's a running gag in the series now to have those same shitty pundits that pollute the airwaves in real life commenting on events in the movie, but it just about made me gag seeing that guy's mug on the big screen (and I get the feeling Iron Man 3 will have the wretched stench of Glenn Beck).