A game where enemies are ONLY activated when light touches them or you get too close. Its possible to get through a level without ever encountering a ghost or entity... The fear is put into the players hands so THEY are solely responsible for how scary it is.
Perhaps could add sound cues to indicate the proximity of a ghost, and add in things that could lead them astray, maybe a section could have the batteries die in the flashlight requiring the player to intensely listen for the sound cues. The ghosts could be smart, and lure the player by making different noises, or open & close certain doors.
its a loose idea, but I think some potential is there :)