Eljasz Weglarz
Eljasz Weglarz voted up Anonymous' answer

I think overt gore is a sign the film maker had zero imagination.  The creepiest films are those that make YOU imagine what's happening, or incite paranoia.

Hitchcock, Vincent Price- that's horror.  I laughed through the "Saw" films, but "Vertigo"?  Ugh.  Some classic Stephen King is also terrifying, because he relied on creepiness of the mind.