1: He has a shitload of gaps in his hair cause look:
He doesn't have big gaps everywhere, they're little. Also, duplicate the hair layer and blur the bottom one, so you can't see the gaps so much.
Besides, the hair is dumb cause I can't imagine that guy going to the barber shop to get a haircut.
2: the skull has a completely different style of shading than the rest, it looks stupid.
Apart from that, they're great.