Just a quick [and unfortunately messy] color edit to give you some ideas on where to go from here. I added a warm highlight and a neutral gray [which reads as cool because all the other colors around it are warm. I find neutral grays to be very visually appealing when used carefully and in context with other colors].

I played with the pixel clusters a little on the face and head to give you an idea of how to really bring out the planes of the face. Plenty of reference images for anatomy are your friend here. Dont be afraid to get in there and emphasize the three-dimensionality of the neck through muscle definition and shape. Consider substituting that black used in the horizontal lines of the background for a dark hue -- by removing this and leaving black in the head [i.e. the foreground object], you are separating foreground and background and creating a sense of depth. This will also help with the 'blocky' effect you were talking about. As a sidenote and for future reference, using horizontal lines in the background like that naturally creates some jagged edges. Trust me, I've had that happen to me plenty of times. :)

Edited by toxotes - 23 October 2012 at 10:54pm

I made a few more edits : I made the right (for the viewer) cheek thiner, modified the right hear, changed the top of the head - which was to big and AA-ed here and there.
I also modified the background and reduced the color count.

Here is the new version:



I proceeded in a most chaotic way and spent too much time on such a little pic, but at last I consider it finished.