As far as horror games go, this is top notch. Despite having no obvious threat, the game manages to build an exquisitely eerie and creepy atmosphere. The little puzzle with the keypad, I felt was reasonably well thought out. Hard enough that I did have stop to take a moment to think about it, but not so difficult that I would need a hint to figure it out.
If you ever decided to expand it and make a full game out of it, I would absolutely pay money for it.