Ive always had a taste for dark book/movies/games, so find the lack of good ones n the amiga a little disappointning. There's a few (already mentioned by other people), but not enough for my tastes. Something inbetween Alone In The Dark and Resident Evil should be doable on a moderately upgraded a1200 (or equiv. aga machine), not to mention '060/ppc + 3d gfx card users.
This isnt to say Id only like a Res. Evil style game as far as this theme goes, but it is something Ive always wanted to see.
Sanitarium (pc game from '98) is a fantastic games too in my opinion, and has a nice creepy atmosphere.