Neatoh :D I like the coloring scheme and style of painting here :D I only have a few suggestions... First off, the white lines of the orbital bones are kind of off... The highlighting of the viewer's left one must be moved farther left, and should have an accompanying shadow to emphasize the muscle mass that's attached in that region. Another issue I have is with the length of the face relative to the nose. If you were to move the highlight that I assume is at the jawbone down father, this proportion would be fixed.

Also, make sure you remember facial anatomy in your highlighting and shading, such as the muscles attached to the jaw, and the convex surface around the mouth created by the ring of muscles there. I don't know any of the proper names for these things, but... Bear with me :)

This is a really cool picture, so I hope you keep it up :)