''God has left the building!'' booms an offstage voice, and Dance plunges into the abyss with a giant ''spoof!'' (just in case the caped ushers and bat-themed Mercedes ads in the lobby weren't enough of a clue-in). Yes, it's a joke, and its punchline is erstwhile Phantom of the Opera Michael Crawford as Count von Krolock, an undead Casanova with an inexplicable thatza-spicy-meat-a-ball accent. Unfortunately, that punchline arrives in Scene 1. What follows is two hours of Moron Rouge, a karaoke casserole of cheap gags, papier-mache sets, and halfhearted pop-song references. (Composer Jim Steinman tries to skip a step to instant camp, draining dry his '80s hit ''Total Eclipse of the Heart'' and tossing in a few Meatloaf references for bad measure.) By the time the vampires really start sucking -- sorry, dancing -- a stiff self-consciousness has set in: It's like watching ''Thriller'' performed by the cast of The Lawrence Welk Show.