The Hangover fits into a category that is somewhat fuzzy and defined as "guy movies". That is, there are few women, there is a lot of male-bonding, and there are wacky, usually R-rated hijinks (well, X-Rated, but what you see in the movie will be R). Also, usually in these movies, the main characters behave stupidly -- or at least hormonally.   We are expected to be forgiving of men in pursuit of women.

In this case, the specific "pursuit" is the time honored bachelor party; and also in this case, wisely limited to the groom, his two closest friends, and a wild-card to-be-brother-in-law who comes along for the ride.  The party, rather than taking place "at a strip club" or even "at various famous places in Vegas" happens instead off camera.  The story picks up in an epically trashed hotel suite.

The groom is missing.  There is a live tiger in the bathroom; a never-explained chicken wanders aimlessly; there is a baby in the closet.  What happened?  Where is the groom, and can the three friends get him back?  What will they learn about themselves when they do?  There is a guy (Ed Helms, who used his natural loss of a tooth do an utterly unnerving "I-lost-a-tooth" effect) who is in a bad relationship.  Will he figure out he deserves better?  There is the absolutely goofy guy (Zach Galifianakis) who has problems relating to people -- will he make it as one-of-the-gang?  There is the cool-friend (Bradley Cooper) who feels he sort of made a mistake when he got married -- will he learn to appreciate what he has got?

And will they ever find the groom (Justin Bartha, who appears only at the beginning and end of the movie) alive?

It is a comedy and not an especially dark one, so you can figure out those answers yourself.  However, and most meaningfully, on the way to those answers -- is it funny? Yes.  It is hilarious.  The Hangover does not rely on being especially clever as it is not. The humor is not sophisticated, but rarely stoops to slapstick.  The surreal nature of the situation, the boys-night-out-turned-up-to-11, gives it enough of an engine that it keeps on moving without having to resort to humiliating its principals for laughs or to the lowest-common-denominator humor.  I was waiting for the gross-out jokes, and there, thankfully, weren't many.

For its genre, The Hangover is a good spirited, comparatively intelligent, well orchestrated piece of work.  It doesn't reach anything like a lofty height, or even a height itself, but certainly avoids the bottom of the barrel.  For a movie category that usually lives down there?  I give it a B.

You will want to stay through the credits to see the photos showing what happened during the guy's black-out.  It's worth watching, and yes, Zach Galifianakis' scene in the elevator is prosthesis -- at least according to Wikipedia.