Funny but not as good as the first one.
If you have not watched the first movie in this series, go buy/rent that instead. This has sort of the same plot with the same cast, the only major difference is that is it in Thailand, and the crazy events are not as spectacular as they were in Las Vegas.
The cast in general does a pretty decent job, but Zach Galifianakis' character has just been turned up another notch on the crazy part. In my opinion this is to a point where it is hurting the movie. I know his career is based on his abnormally grotesque humour, but I would like to see him in an very different role for once.
Watch if if you like high budget slapstick comedy. I would recommend you watch it with a couple of like-minded friends along with a couple of beers.