I like games in the same vain that have deep lore and a very dark atmosphere in a troubled and violet world.
I took my sweet time exploring most hallways in all three games and reading every note and hearing every textlog. I LOVED both Amnesia and Outlast and finished them all.
Especially the part where you are defenseless but still constantly in danger is very rare in games and few games do it successfully like Outlast and Amnesia : The Dark Descent. I have no truly similar games to recommend, but I do have good games that share SOME similarities with them, but not that much. These three games exemplify three very different types of horror. Very few games are as eerily horrifying as Amnesia : The Dark Descent, or as poethically dreadful as A Machine for Pigs or heart-pounding intense as Outlast.