You wouldn't think a minor twist could make such a difference to a fundamentally formulaic slasher movie. But swapping cute guys for the pretty girls who usually wind up on the business end of some psycho-killer's blade does the trick in this handsomely styled horror picture, which also makes a good-faith effort to differentiate among the victims-to-be before it starts picking them off. It's the night before Halloween, and two gay teenagers necking in a Los Angeles park are brutally slain with a scythe, their heads taken from the scene by the killer. The next day, four roommates meet up before the West Hollywood Halloween carnival. En route to their night of costumed...