I recommend The Legacy: Realm of Terror
I must warn you though, it's pretty hardcore, without a walkthrough, you may end up needing a few months of experimentation to finish it; luckily, there is a walkthrough in Youtube to help you if you get stuck.
You play as a hapless individual who inherited a huge mansion, but cobwebs and rats are the least of your worries. It is obvious, right from the start, that something has gone terribly wrong in that place. We are talking Lovecraftian mayhem.
It's a retro survival horror slow FPS affair, with your character moving through the house, while avoiding dangerous foes until you find enough resources to defeat them. The first half of the game feels quite nightmarish, as your character constantly gets paralyzed by fear, your ammunition is scarce, your combat abilities are terrible, and the puzzles are quite cryptic.
The mansion is also filled with hidden passageways, one way doors and teleporters; dangerous areas you normally shouldn't be able to access in more forgiving games, are available from the very start. I love it all!
The only thing that bugs me, is that by the end of the game, if you have been upgrading your character right, and if you have managed to get your hands on some very powerful items, the fear is greatly reduced; you feel like an enhanced version of Ashley Williams, destroying foul creatures through melee and magic. I would have prefered it if the tension was kept up to the very end.
It's a flawed gem, but one I am very glad I got to enjoy; get it if you like an unforgiving experience with an entertaining story, NPC interaction and slightly confusing maps.