I have to agree with Grimsane that the shading of the forehead is subpar compared to the rest. The asymmetry of the nostrils is only very noticeable to me if I zoom the pic, but at normal view I wouldn't call it problematic. Actually I think it could be fixed by moving on the left (his right) one pixel over to the left.
Whaddya know, the shadow of the glasses actually does add depth to the piece. Good call!
The shading of the cheeks kinds of make his head look slighty tilted where it was head on before. Alternatively, it makes him look like one side of his face is thin/angular and the other side round. I say dial back on the shadow on the right side and shape it to match the left side based on that great guide Grimsane made.
You definitely have reason to be happy with what you've got now. Whether you consider this finished or not, great improvement. I hope you'll be able to apply what you've learned to future works!
