be careful of lumpy surfaces as it reads poorly (like the temporal/zygomatic area on ur latest head). try shift the light around in zbrush so you can see exactly what the surface is doing. would be nice to see you push the forms more to get a more expressive stylized look.
tho cool style, cant see anything fundamentally wrong anatomy wise. seems you have grasped the major forms..i guess just have fun with it and keep posting heads for further improvement!