Nice pixel! However, the head doesn't really seem to 'pop', and around his mouth, probably due to the similar colours used for both the teeth and the rest of the bone, they blend a little. Also... the shading at the top of the skull makes it seem a little flat. I'm not sure, but maybe shading that the same as the rest of the face would improve it? Other than that, it's rather good.
-Ragnarok