Wonderfully simple! I see a lot of people using that word for this little game here but it's really the best way to describe it! Simple! In gameplay, execution, even the casual way they hit you with the 'horror' part of the experience!
That's what really makes these so unnerving, I find! and I can't get enough of it!
One more thing though, I absolutely love the little alternate ending you can get. Absolutely genius.