@aska, cute idea, I can see the little guy is pretty scared by something!
I'm no expert, but I'm thinking maybe working on the shadows could make the image read better. I wasn't sure where the light source was based on where the shadows hit. Softer transitions might look nice too, between the lights and darks, but maybe you were going for a more "graphic novel" style. If so, then you have it right with distinct darks and lights.
Hope that helps a little!