mapping is off, straight lines on flat dont map straight on the head.
not enough definition between the plates, you blur things out with ridiculous amounts of shadowing.
your work in general is always a bit too choppy and messy for my liking.
might be because you try making curves with a series of straight lines, or because of the way you use curves and straight lines together, or the way you shade things like theyr straight lines instead of matching the curves.
i dunno