Unnerving.
The hair on the back of my neck stood on end at one point, and I had several chills go down my spine. This song radiates a melancholic, yet disturbing and tortured aura. Unspeakable evil born from innocence and plain curiosity, and a corruption and degeneration of the soul far worse than death itself.
Just what Anubisblack said. I couldn't have woven the despair and subdued malevolence of the song into better words than he did.