I'm definitely a wimp when it comes to horror, but this game is, I think, terrifying by any standard. Though it might possibly have something to do with the fact that I played it while completely alone at 11 o'clock at night. Anyway, the basic premise of the game is that you're in bed, and you hear a strange noise. How you investigate it is up to you, but I can assure you that every mundane action you take becomes unbearably suspenseful (aided in no small part by really atmospheric text design), mirroring the sense of jumpy anticipation one feels when traversing their house in the dead of night. You're always expecting something terrifying to happen, and when it does, it's always in the subtlest, creepiest way it could be. So please do not be like me and play this game at night (or do, if you want to be really spooked. Just keep some lights on somewhere.)
In short, very well-written and designed horror game that uses all the right ways to scare the crap out of you without relying on cheap tricks or even any sound (not that I don't like it when games use sound, but it's impressive that this game managed to put me so on edge without it); the only drawback, I think, is that it is very short and I couldn't help but feel disappointed when I felt that I had exhausted the limited supply of options to explore-- that definitely deflated the scare factor for me, but I was still impressed overall.
Edit: When I wrote the review, I hadn't yet found a way to "win" (that is, survive the night). I found the ending somewhat anticlimactic, but it did fit in with minimalistic style of the game-- as well as making my overall impression of the game more satisfactory.