I must be one of the few people who were disappointed. I went to see Iron Man 2 less than 24 hours ago, and... well...
The character development felt awkward and stilted in many places, the character of Justin Hammer must be one of the most brain-liquifyingly annoying people I've ever witnessed in a movie, Scarlet Johannsen (or however you spell that) managed to cement my conviction that merely looking good just doesn't cut it when you're trying to bring a comicbook character to life, there were some horribly dull lengths during the middle (seriously, cutting away about 20-25 minutes would have improved the movie), the interesting (and in some places really fun) bad guy got the short straw regarding well-used screentime, and they managed the impossible by not making Nick Fury - played by Samuel L. Bad Mutherfucker Jackson - look cool.
The movie did have its strengths, too, with solid action, an aforementioned altogether more interesting villain, some juicy tidbits for the fans (like the suitcase) and, of course, the introduction of War Machine... but these bits were in the minority, and the drastic decrease in levity didn't help the main character either, even though I understand that it was pivotal to the new plot.
Maybe this is one of those movies that get more enjoyable the second or third time around, but for now - and let me state that this, just like everything else in this post, is my humble opinion - I can't help but feel that Iron Man 2 reached for the extremely highly-set bar raised by its predecessor, fumbled spectacularly and broke at least one of its armored feet upon landing.