Yes the hair is a problem. That is considered a bad pixelart technique and you'll only be embarrased in the future if its in your gallery.

Also this piece like the other head you have in the queue could be improved with more contrast to the face or better definitions and even some adjustments in 1 or 2 of the flesh tones.

I think a forum WIP thread could help you.

I think that sculpting the face with contrast of lighted and shaded areas is a right way, but not be too carried away with all the details or face will look older than it should be.

And what Kam!! said about hair.

 Ok, I got it, i will improve, thankr for the suggestions.

You have some issues when it comes to shading the hair. What you did is what we pixel artists call "pillowshading"; basically, it's putting the lightest shades in the middle and the darkest shades at the edges. The end result looks incredibly unrealistic.

What you have to do to fix this is simple. Figure out where your lightsource is. (Judging by the symmetrical face shading, I'm assuming it's from directly above you.) Then, shade the hair by determining where the light would hit it. Don't worry about shading the strands of hair individually, just shade the object as a whole.

There are a couple of anatomy issues, but I'm not the best person to ask about that. My main problem is how low down the mouth is; it should be a bit higher up.

Finally, you may want to screw around with the background colors; the blue shirt really clashes with the green background.

But all in all it's pretty good.