Pretty nice
I started at making a kinda cartoonish set with almost same style as this head but alot simpeler just because i liked it that way.
But to your texture:
Drop shadow could be added a little darker
That white in the iris its nice but too visible to me maybe blur it a bit?
Also try shade the glasses a little and that little hair under the mouth(dont know its name anymore)
And with shading i mean just add a little something a little lighting or shadowing would make it already alot better