My wife and I saw it on Saturday. I was prepared to be underwhelmed because, well, it's a sequel, but I came out feeling quite good about the movie. I like how it extended the mythic structure of the "maker-warrior," delving deeper into Tony Stark's internal demons while at the same time introducing new challenges.
Robert Downey Jr. does an outstanding job as Tony. Don Cheadle is solid as his best friend Lt. Col. Rhoades. Sam Rockwell is both funny and swarmy at the same time.
That's not to say the movie was without flaws. In my humble opinion, IM2 suffers the same setbacks as the original, namely (A) a lack of chemistry between Stark and his love-interest/girl-friday Pepper Potts, and (B) epic fail on the big "boss" fights.
Overall, I highly recommend Iron Man 2.