Number one is that it just scares people! Your hair is standing up on your arms, or at least that there's a few moments when you're jumping. That's what makes it a good horror movie.
I think suspense is a big thing.
It's up to each person's parents whether they think it's too frightening or too violent, how much their kids can handle, what they want to teach them, what they want to show them.
All these horror movies are slasher film now. I like them, they're fun, but they wink at the audience and you're really not terrified through the movie.
I'm a horror movie fanatic.