First off, you have a very original and unique artistic style.
I simply love the shades of grey, they are eerily beautiful and yet so expressive. I also love the facial expression and your use of sharp angles. So many people tend to over do it with the angles, but you have definitely succeeded in balancing your piece.
I also love the facial expression, its so solemn and full of despair... as if his hamster died.
As for suggestions, I would perhaps detail his hair and clothing a bit more. However; part of your style is the haphazard blending. So perhaps you shouldn't change anything.