Simply put, Amnesia should use the same approach to true psychological horror as Penumbra did - create a sense of utter solitude, paranoia and dread. Scares should be few and far between and should come really unexpected. The part when the Tuurngait burst out of the closet near the storage room was predictable, I already heard him in there. I knew what was coming when I was passing the door for the last time. Still, the Infected guy's entry was so abrupt, sudden and crude, that I literally jumped !
One really good way to create unexpected "closet scares" is by giving the player a feel of false reassurance, subverting his usual expectations : "Oh, I'm in a brightly lit room now. Nothing can happen, nothing could possibly go wron... Aaaaa !!!!"
: Or make that a half-lit, half-dark room. I, personally, am not very scared of complete darkness, nor overly lit spaces. It's the half-lit ones that really feed the fear-inducing corners of my imagination. A room nearly flooded in darkness, with only a weak yellowish light of an old lamp here and there, is one of the best sources of paranoia fuel I can think of.
For example : I replayed BP's Kennel level yesterday night... Once I got to the "run like hell and stay in the light corridor", I felt shivers down my spine. I was never as scared by any other level in the series as I was while running through that nightmarish corridor... First, you found the notes about that researcher-turned-cannibalistic-monstrosity. Then you entered the nearly pitch-black corridor and you heard every damned moan, roar and shreek of his behind your back. You knew about his weakness being light and you knew that the malfunctioning lamps were your only lifeline... When I first started to run, I miscalculated and suddenly became engulfed by the dark. In less than a second, that freak was already attacking me from the back, ready to tear my head off...
If there's a specific sequence in the whole Penumbra series that scared me the most, it was this one. It was completely horrifying on every possible level... Damn those talented young Swedes !
Sorry for the longer post, I just had an urge to write something insightful about game atmosphere...
"You... silly Billy !" (Clarence, Penumbra : Black Plague)