Stylistic omissions
Removed the definition of the chin.
Made the chin pointy.
Removed extra detail on the nose.
Shrunk the lip some.
General improvements
The head is too triangular. Ideally, you want a head that resembles an acorn. The subtle difference between the two shapes makes or breaks the facial structure.
Rounded the eyes some.
Darkened the lashes and gave them a more angular shape.
Rounded the top of the head and hair.
Things I did out of personal preference
I'm not an oval eye guy/suck at making oval eyes.
On the subject of tablet calibration,
Pressure Curve Tool is awesome.