Sinister is a very good word to describe this. Very accurate indeed.
I happen to think the beginning was a bit slow. I liked the sound of it, though it seemed to me to drag on forever.
Although I didn't appreciate the bit of silence there, the laugh there more than made up for it. I will admit that I got creeped out by that. Very nice!
Afterward, likin' the buildup. The bells add to the dark and sinister atmosphere. I didn't much like the ear piercing from hearing them, though they were a good addition.