The pillowshaded highlight in his hair is really ugly. I wish you would've broken up the highlight with it following a few strangs here and there, rather than looking like it's all one mass. You really went to far with the aa on it, I think, the lines for the lips and nose especially look blurred.
I really like the zombie though. I think he'd benefit from some more contrasting shadows (not says to change the colors, just apply the dark brown or the gray in the skin more liberally) and broader shoulders though.