I just finished the last level of Portal and yeah, those end credits are really funny! The game has a good sense of humor through the whole thing, and the credits pay off a couple of running jokes in the game.

I guess it took me about three-four hours to get through the entire thing, and there are advanced levels and achievements to go for, etc., so I could probably squeeze two more hours out of it. Five-six hours for twenty bucks, I dunno.