Looks amazing! The only thing you could do to make it better would be to be more careful with the lasso tool cause sometimes it makes your shading choppy.
I love it! But I agree with Helen, lasso tool makes shading look too sharp. I have same problem in photoshop too /:
You just have to take it slowly and try to make more rounded lines is all.
Sorry but what is the lasso tool ? .... amazing graphic , but i think you have to fix the eyes little bit .