You don't have to post something at x4 the size we can just click on it to zoom in if we want.
I traced over to show about where I think the eyes, ears, nose and mouth should be ( in green ) and how the shape of the skull should look.
The ear is way too far back and too small.
The eye pupil doesn't quite work, it needs some refinement, although it's hard to do with that limited space. Right now it looks like he's bug-eyed or on drugs.
The black around the mouth is confusing, why so dark there when under the chin is not that dark?
There is a purple line running down the neck that I don't understand why it's there.
The yellow on the front of the face and forehead makes it look like he's staring into headlights at night or something. You need to tone that down a bit, unless that's what you want.
The collar is confusing because of the lighting, the highlight's coming from the back when it's coming from the top-front everywhere else. Also the shape of the collar doesn't really have any indication it's clothing, no folds and it's laying kinda strange.
The shadow under the chin and behind the hair is too dark, it draws the attention to those spots too much and doesn't look natural.
After having said all that, the face does have some nice character to it, I think if you fix those points above and maybe find some good reference this could look pretty cool.
