The phrase "bachelor party in Vegas" suggests a specific sort of movie — a raunchfest filled with booze, babes and fratboy delirium.
"The Hangover" is a more interesting and much funnier film. The four friends it follows from their native Los Angeles to the desert casino kingdom are in their early thirties, so they're well-defined personalities. Doug (Justin Bartha), the groom-to-be, is an amiable straight arrow, and his two best friends are likewise nice guys: Phil (Bradley Cooper) is a teacher who loves his wife and kid, and Stu (Ed Helms) is an excitable dentist with a girlfriend, alas, from hell. The only wild card is burly, bearded Alan (Zach Galifianakis), Doug's soon-to-be brother-in-law. Alan appears possibly to have been hit in the head with a shovel earlier in life. He says things like, "I'm not supposed to be within 20 feet of a school." He's worrisome.