Here's an edit explaining what I mean about clean-ness. Mainly look at the head. You can go as filthy as you want, but it's all texture. The idea is, there is ONE, DEFINED COUNTOUR at all times. Go nuts INSIDE the form, but the form should always pop out and be easily communicated to the viewer. I explained what I ment about the bent arm too, and rearranged the fingers in a more probable position. You should never work on a white background. It's impossible to colour properly, everything comes out too bright. Also, a character such as this should be worked even from pure black, so as to be more threatening. I also do not know who this character is, so excuse me if I didn't remain too faithful. I think for example, that the eyes really add to it.
Hope you don't mind the edit.