Yeah it's a great game. Trying to play their earlier effort Penumbra: Black Overture just now - not just as polished as Amnesia and a bit frustrating at times but the atmosphere is good and I'm intrigued to see just what the hell is going on - love the 'spiders' part of the story...
I have to get back to the earlier ones at some point. I played far too many mods & the main A:TDD story followed by Justine, by time I got to the prequels, was a bit burnt out.
Definitely not as polished as Amnesia, but still good.