I agree that a little dithering will give the afro texture. As shaded right now, especially with that highlight on his left side, my mind jumps to the Bride of Frankenstein.
I'm thinking you don't want to use too many colors, but I think you should choose another color for the shirt--right now it blends into his skin and made me think he was shirtless. Also, the facial features could be outlined a little darker... ? I dunno.
It's really hard to be objective here, since afros == <3 for me. Good piece overall.

EDIT: Actually, I decided to do a quick edit:

Actually working with the piece, I think there are too
many colors instead of too few. Also I think the color of the hair could use more contrast.
I might have made him look a little older than you wanted him to be though.
