I really like this arwork. I feel that you have given a cler 3-d perspective with your use of shading and the white line. I feel the symbolism is very powerful, and you could definately take this further. My only quip is that the piece is not realistic enough. If you were to create an improved version I would suggest that paints or pastels would be better then a computer for the level of detail you could include.
Overall a wonderful piece of work.