That popping vein..shouldn't really be there, since he's thumb is up and smiling. Do some shading in his nose[or whatever you call that] so we can understand that it has a tube form, and not be flat. His eyes are abit off, looks like he's missing a screw or two :)
Needs alot more contrast on his pink body, and a little more saturation as well i'd say. Maybe add in one contrasted highlight color, as to give it a good cell-shaded look. Also take off the line over the right eye, it makes it look pretty weird. The hand could use some work as well.
