If you expect better than the first one, you gonna be disappointed...BUT:

Rating: 6/10 (15 June 2011)

if you expect to be entertained, well, you gonna have fun.
HangOver 1 is one of the best mature comedies I've ever seen and probably no one could have topped that or even remained on the same level. The movie is actually so much of a remake that the storyline is just put on a different location, some dialogues became rewritten and you are done.
Nevertheless, ONLY if you expect the same superb movie than the first part was you will be disappointed! I personally had a few really good laughs out of it and had a good time, but I've read that some people downgraded that movie because it was not on the same level than #1. This is plain wrong, because Hangover 2 STILL outshines lots of other comedies out there!