I think overall its a great piece, but maybe put a bit of extra dithering, that would make it look clean and finnished.

Thanks for putting effort in comment, it was very helpful!

With this much work on the background it might have been better without it. The ice is nice! Most of the guy I like too, but the shading on his right hand is a bit off, and what is going on with his left shoulder? Did the evil docter not put it in place correctly? ;)
At last, the hat.. This is also something you might want to go over, why is the top dark and the side bright?

Keep the contrast up, the size down and you will be doing fine :)