I'm not a huge fan of the dithering, and the shading on the shirt is much too ambiguous, it looks like he's wearing a potato sack. the teeth lack definition, maybe go back with a darker tone and fill them out so they look like a set of chompers instead of scrambled eggs. The shape of the head could be a little more interesting too, it would make the character have more of a personality if it weren't just a simple circle. Also, the highlights in the eyes would look better if they were the same shape. maybe give him some hands?
The overall piece has potential, it's an interesting character. he did make me chuckle.
