Went to the midnight premier and thought it was very good. The first is still better because of the character arc, but for a second sequel this was well done and entertaining. I really, really liked how they handled the Mandarin, it was a clever and somewhat daring choice and an excellent commentary piece. The film never hooked me like the first one did but that's a pretty high bar to match. I was glad to see that for the first time they actually gave Pepper Pots something to do instead of simply being Tony Stark's girlfriend. I was a bit sad there was no credits tease for the next film like the previous Marvel films--maybe they did that just as a lead-up to Avengers--but there a short and fun bit after the credits are over that is worth staying for.
I get the feeling by the end of the movie that they might be setting this up as the last film in the Robert Downey Jr Iron Man series, barring his appearance in Avengers 2. They could certainly do a fourth, but I think Downey might be getting a bit tired of the role having played it four times times as it is.
I saw it in 3D and IMAX, the 3D was well done and surprisingly subtle, I would recommend it for those who enjoy that format.