Great atmosphere, excellent graphics and a chilling story to tie everything together.
The atmosphere and story combine well to create an unforgettable experience, and the difficulty is set just right to make it challenging but not frustrating. By atmosphere, I mean excellent graphics and sound quality. If by that alone, I would have given the game a higher rating. The game played well enough to make me want to play it thrice (I was going for the platinum).
My only problem with the game is that it can at times get monotonous: you see the same creatures over and over, level after level, and while it's obvious they tried to provide variety, I still got the feeling I was fighting the same monsters repeatedly. Also, not to nitpick -- the main character seemed a bit too detached: all the tension going on and still not a peep out of him. He was silent throughout, and while I realize this is by design and contributes to the creepy atmosphere..... it still not realistic.
Nevertheless, this is still an instant classic for me. The production quality still measures up relatively well in this day where we already have the sequel, Uncharted 3, and L.A. Noire. I can't wait to play the sequel!