I am fascinated by games with 2D art that still manage to give you a good scare. I guess what I find interesting is if a game can manage to translate the scares and audio design which we know from 3D environments and movies. I have never really played any though. I would love to hear some suggestions, especially with Halloween coming soon!
Darkwood, Fear & Hunger and Faith are some of the spookiest games I've played, and they are all 2D. They create horror via suspense and dread instead of just jump scares.
Seconding darkwood - one of the few that matches Amnesia in its ability to make you fear what you cannot, should not see. You pray to whatever gods you believe in that your light lasts and that thing that goes bump in the night does only that.