I didn't realize there are so many games so similar. Still, none I've seen so far comes close to Amnesia.
What I would recommend is a game that was only recently replaced by Amnesia for my "scariest game ever" choice:
System Shock 2. The only thing it has in common is the general horror atmosphere and sense of loneliness paired with a first-person perspective. Otherwise, it's very different.
A sci-fi RPG set on a broken space ship, trillions of miles from earth. There
is combat, a much more complex RPG system... but, like all the games that are doing horror well, it's the
amazing sound design that does the job. It has those moments where you stand in front of a door, hearing some scary voices on the other side and you just
can't walk through it. Very recommendable.
Intro
Vid with high-res mods installed (it's a 1999 game!).