Why is amnesia so awesome?

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Amnesia and Penumbra focus on immersing the player into their respective worlds. IMO, they certainly did a good job of doing so. i just started playing amnesia, though i haven't gotten very far, and it is already much scarier than the demo. So what "makes" the game experience for you? if you could pick any aspect of amnesia that would be your favorite and did the best job of making the game enjoyable, or just a better experience for you, what would it be? personally, i really enjoyed the audio in the game. the sound design is incredible, and i would say the combination of the unequaled audio design and the atmosphere definitely has made this game stupidly scary so far.