so i tried touching i a bit, and i realize a lot of people are in this thread, but i thought i had a few observations to add.
first off i think i have to agree with helm that the light hitting the face is far too symmetrical and it makes it look a bit robotic. I just went with sort of an oncoming - slightly to the left light source i guess, and hoped that would allow for enough variation in where the light hits to make it look less symmetrical.
Next obvservation - immediately, the eye whites come through to obright. i think your third lightest shade is a bit too dark, and your second lightest skin tone is a bit too light (what you are using). So i edited the eye a good bit on the left side, but the way i shaded it would probably have been far more appropriate for the right eye. I tried a few combinations and i felt personally that putting the second lightest value in the eyewhite closest to the nose and the third lightest value on the outside eyewhite gave the most realistic effect.
I think the cheeks look a bit overshadowed in most of the renditions, it feels like unless the light source was close to the face and topdown (three quarter angle), the cheek bases would look just a bit lighter as they approach the jawline, where the drop off in value is rather quick, not gradual.
The skin above the upper lip i gave some more highlight to accentuate that feature and make it more pronounced as it usually is on people.
The eyebrows look too straight for comfort for me so i just added a tad bit of softening above the eyebrows edges to make it look slanted. this changed how i highlighted the brow structure on the forehead, and also added a bit of a dip between the ridges to depress that part of the skull a tad.
the hair - not really sure i like the dithering of the lightest value in that highlight area. instead, i think it would look more appropriate to make it look shiny first to indicate there is a skin covered scalp up there, and then just give it some hint of texture to indicate hair growth, but thats assuming youre intending the hair to look pretty short, which is how i interpreted it.
and lastly, for the nect i think it needs to be way softer than you are illustrating, looks like youve stripped off the skin to expose the inner tendons and tissue.
I dont think my version is perfect but i think that it diminishes the otherwise timid/scared look on his face into something a bit more relaxed.
hope this helps rather than not.
