The atmosphere is chilling and sinister, accentuated by the best when it comes to sound design and music, as well as the dark art direction. The thumps of the percussion when the enemy nears and its growl are very fear-inducing.
Enemy design will be a point of debate, I feel. Interesting that it's an implicit NPC, represented only by a colour, but the way it captures you can be abrupt and unavoidable. I also wasn't initially sure what the rocks did, but assume it has some sort of relationship with negating the enemy (this can be driven home better, though, as it didn't work much of the time).
Navigation is also an uncertainty, as there's little in the way of guides as to where you should be going once flipping all of the required switches. A lot of the time, the enemy catches you as you're turned around running away, so I pretty much got stuck in one section early on and couldn't advance past that point (and the checkpoint is unforgiving).
Functionality is impressive. I know this game is a stride for the developer, who's inarguably one of the best 3D artists on the scene (though, would love to know what was the inspiration behind the low-res and basic art style).