Seems to me the nose and eyes are a bit soft and low contrast, probably through being not quite in focus. The left ear and the hairs on the top and back of the head are sharp, then it starts to fade again. The right ear looks a bit odd to me, almost as though oversharpened, it might be due to the change in colour around the edge.
The bokeh is very nice, very smooth background, which is partly what you pay for in a good lens.

So I think probably it is dof problem, compounded by the point of sharp focus being not in quite the right place.

I wonder also if it would benefit from brightening up a touch in software.