i'm at work, so i can only offer up a quick crit.
the texture looks blurry around the nose.
the cheekbone looks... weird
above the eyebrow the colours need to blend more
the creases of the eyebrow above the nose look to sharp to me
you could add a few brow lines, his forehead doesn't look as old as the rest of him
having said all that, i know its a WIP, so you might have been about to address all that anyway.
great mouth BTW
what i would say is that i prefer going for a full face unwrap, and a mirrored side of head, that way you can add all sorts of asymetrical detail to your texture. however, if you don't have space for that in your spec, then half a face is perfectly understandable.
I don't have a sig, live with it.