You've got some solid outlines there but the shading lacks definition. It isn't clear where the light comes from and it looks mirrored. That can sometimes be good, and sometimes be bad. In this case it creates the effect of almost-pillow-shading and that is something we don't want to go for. The picture would also benefit from a little more contrast in the palette and maybe a hue shift here and there to make it look more interesting. Nice effort though. After all one doesn't have to be ashamed to have this as a sprite in a game.