I just saw Iron Man 2. I think it was a solid sequel, but not a great one. But that's still pretty good, when one considers the history of awful Hollywood sequels (Star Trek V, Jaws IV, Rocky IV, Crystal Skulls, etc.)
There's a few problems with the movie: (1)There's not much tension or suspense, I was never on the edge of my seat.(2) The snarky back and forth between Stark and Potts is a little old. (3) Rourke doesn't make a good bad guy--not because he isn't a good actor, but because we like him, which is probably why there isn't much tension. Hopefully Mandarin will be someone we feel comfortable hating! (4) The drone robots aren't that menacing. They're basically like stormtroopers, minor nuisances, predictable losers. (5) As many people have noted, the fight scene with Whiplash, Iron Man, and War Machine is way too quick (again, lack of tension and suspense).
There's also a lot of stuff that's good in the movie: (1) I think Cheadle does a good job, considering he's replacing someone everyone liked in the first movie. (2) Black Widow's fight scene was pretty damn good. (3) Justin Hammer is funny, but not to the point of detracting from the movie. (4) I think Samuel L. Jackson did a very good job, considering his character is, to this point, undeveloped. (5) Thor's hammer at the end. Wow, I just hope Thor is a gritty, dark movie, without too much cornball. If Branaugh and Hemsworth pull Thor off, they'll be my fav director and actor of all time!
All in all, Iron Man 2 is a fun ride and a worthy sequel. Could have been a bit better, but the first Iron Man was just soooo damn good, I don't blame them for not being able to top it.