First few things I notice:
- The eyes should be about half way from the top of the head to the bottom of the chin. Of course there are no "rules", but if they are farther up then the character looks kind of mongoloid. Yours are 5/9ths up the way of the head, and it is negatively impacting the look in my opinion
- Dithering does not work well for skin. I find that usually when something has definite and obvious lines, as in your top left colored one, then it is because there are flaws in the shading, and/or the colors are poorly chosen. It can work, don't get me wrong, but usually it makes the texture too grainy to look like skin, and the whole piece just looks muddled because of it.
- You have nothing indicating an eye lid and eyelashes and such. It's like the color of the skin around the eye transfers directly into the white of the eye, and it makes it look like the eyes are totally flat and glued onto the face. You can see Altoontoon addressed this in his edit.
- Having the bottom of the pupil visible, but the top hidden gives the impression of looking up. Not sure if you want this.
- In natural light, the upper lip is darker then the bottom one. Your mouth looks kind of plastered onto the face, similar the the problem with the eyes. One thing may be too great a shadow underneath the bottom lip.
- Seems to be too many colors. 9 colors for just the skin? Again like I said about dithering, often when there is a flaw in the color scheme then the only way to make it look alright is to add in more and more intermediary colors. However this will make it look, "pillowy" as yours kind of does.
I'm not sure if the workflow you are using, making a planar type model is good or not. If it helps you then use it I guess, but always remember the bottom line, making it look how you imagine. Anyway keep it up, seems you are pretty dedicated.