Pretty captivating.
There's some pretty cool visuals meshed into this. I like the figure clawing at their own face, sharp teeth, with the tongue thing in the top right, and I also like mouth eyes in the bottom left.
But there's some pretty goofy/wacky looking faces or details that shift it away from being completely menacing. The oversized nose, middle bottom, for example looks moreso funny, especially with his fu man chu tentacle-stache. The very top-right, bug-eyed grin thing that's sort of a mix of Hellsing with Trollface is a little goofy lookin' too, but that might be because of the styles of teeth. You have a portrait of different maws all over the place here. Some human looking teeth among sharp, demonic teeth...but up in the top-right, at least, you have cartoon piano keys. See what I mean?
There's also many missed opportunities to make use of shadows to your advantage. Blur your eyes looking at this and focus on blackness. Some of the coolest features are engulfed or incorporate shadows...ESPECIALLY the bottom right half-face (really cool and atmospheric), the two in the top left, the scream face with a figure in it's mouth, and the one I pointed out was one of my favorites (face clawing). If you incorporated MORE shadows into this piece, it would have been more eye-grabbing, because the faces would pop out...even if it were as simple as a burn tool or just shading appropriately in between faces...it might be too light. That top right section could use just as much or more shadows as the bottom right section has. See what I mean?
If you want dark...go for DARK, and see how subtle lighting can help things in the scary shadows pop out...if only just enough to be noticed. It would improve the intended atmosphere you were going for here tremendously.
Voted 5! :D