The atmosphere feels great. Looks and sounds match up, although the walking sound still plays for a bit after the player stopped moving.
Sometimes it confusing when you got a key and want to open a door, but this keys wont unlock it.
You could change the color of the locks accordingly to the color of their corresponding keys.
Additionally you can see the keys through the walls, (maybe this is a bug) but I found it useful, because you can get a sense of where you might go, instead of stumpling around in the darkness.