Good movie.
I saw it at midnight with some friends yesterday, and enjoyed it about as much as the first one.
Keep in mind, I'm not a huge Iron Man fan from the comics, but he's an enjoyable character, and Downey absolutely NAILS him.
Personally, I'm waiting for the Captain America movie that's due for release next summer. That'll be the next big movie for me. HUGE Cap fan.
By the way, don't leave before the end of the credits. They're clearly building towards the Avengers movie, which is due in 2012.