eyes:
Try to make your eyes more "real"with the whites of the eyes, the iris and pupil.
Feels a strong flare, a little strange ... the white looks kind pixelada.Tente add depth around the eyes, it seems who are floating.
Skin:
Try adding some features a bit of light and shade so thin cheeks.
Nose:
try lowering the nose and do the "pipe" of the nose with a little shade. phlegm that drips do not make much sense ... Try to make it smaller and a little inside of the nose and increase the opacity add light and shadow.
The mouth:
The mouth is good but remove the shadow from the top of the mouth ... I think that zombies do not have white teeth.
Add light and shadow to the teeth and tongue, try different teeth because the teeth of our mouths are not equal.
the spittle this very opacity the opacity and place light and shadow.
and try to put it a little more into his mouth.
Hair:
Do not use symmetry in the hair, our hair is not totally equal on both sides.

Everything is too pixelated.3/10
Try next time to save preview in png.