Skull Guy

I like how the obscure the face is in the image, plus the single red eye shining brightly, seeming to be glaring at something. I also like the different take you have on the depiction of a skull.

Now, there are a couple of things you could do that can really make this "skull" more menacing. The right side of face looks interesting, but left seems a little less detailed. Maybe adding the same hole shape/red eye or similar on the other side of the skull will help it look more complete.

As for the background, I think a little more detail in the atmosphere can be added. To me, it looks like you took the gradient tool with the radial option and just used that only in the background. Adding a little more splotches of color and some slight texture can really help bring a more dark looking background.

Other than that, great use of style and work on the skull! I hope my critique has helped you. ^^