I'd say this piece suffers from overuse of and unnecessary dithering. If you use dithering improperly your image will often look grainy/textured were there isn't any grain in real life (ie skin is smooth). An edit to show you what i mean:
Your's on the right mine on the left.
Take the time to look at how your a piece would be without dithering and ask yourself if it's necessary or not and if it isn't don't do it.
Other than that good job at rendering the forms of your face.
