Whoa you pay a lot of attention to lighting details!
One thing I might suggest is to perhaps use a little less shading than you are doing now. What I mean is that I often find the shading value you use for clothes, skin tone and hair are very similar, giving the impression that they're the same color. Maybe use a different pattern of hatching for different parts of the person? (Hair, shirt, skin)
Not that they don't look really good already, I just fancy that they'll look even cooler if you try that. Just my two cents.