Question of the Day: What Makes a Good Horror Film?

Wow, I haven't done one of these in a long time. Since I've been thinking about horror films all summer (and will continue to do so) I was thinking about what makes a horror movie great. So, what is it that makes a horror movie great for you? Is it the comfortableness of the genre (i.e. the gore, the violence, the gratuitous nudity, teens in peril, etc.) that gives the viewer the kind of nostalgia that a lot of people opine about when they speak of horror films (specifically the slasher...