I like to see a creepy game, with creepy art style(or not). Nothing violent/gore/scary about it, but it has a very unsettling feel to it. (something out of the normal way of presenting horror games)
Avoid the cliches of horror games, because they're too many and it gets old.
A good storytelling in a horror game is better than just spooks & jumpscares.
By the way, I love FNAF. Great idea, great presentation!