well, don't go overboard with AA, but right now I'd say you're... going underboard. I see a lot of single-dot aa, where 2/3/or 4 pixel-long lines would be more appropriate (check out the 'too little aa' entry in this section of the PJ tutorial). aa is inconsistently applied on the eyes/nose/mouth, being completely absent in some spots. a better range of values (more contrast in your palette) would help it pop as well.
I think this would look a lot better with smoother lines. Try to AA the crap out of it.
cool face nice shadows!