I suggest you to fix the edges and shades of back plate ...
also that icon on ear-plate could be a little bigger, and more complicated, try to add some more details at the front of the head ... nose and mouth area seems to be really empty, fill it with something ...
Try to make some nice details at the top of the head, do mapping well and it will be epic ...
Back to the back-plate ... do those tribial things more contrast and darker so i can see them better ...
i think you're at good way of making an epic head if you will work with it for some more time ...
for me 9/10 but make those little details working well or it will drop to like 6/10 :P