Saw the 1am showing, wow.... I was expecting a decent movie, 7 out of 10'ish. But Hangover was great, like really great, 9.5 out of 10 great. IMO better then a lot of the recent comedy classics, Wedding Crashers, Dodgeball, Seth Rogen stuff, etc. It had a fresh intro, the plot was pretty unique, and for a movie, almost everything was semi-plausible.
I also heard that the previews gave all the good parts away, definitely not even close.