Thanks for the critique, milleja46. Although I actually think the lighting on the cheek is pretty consistent with the rest of the piece... If you'd like to do an edit to show me more specifically what you think could be improved, I'd be happy to take a look.
Thanks, Mathias! I chose this direction to try and push myself in terms of lighting organic volumes. Despite the level of detail, I'd like to avoid pure realism, so I share your concern about taking it too far from the original sketch. Hopefully I'll arrive at a style we both enjoy.
The only reason for the tight cropping is to challenge myself to compose a nice portrait within the confines of a 64x64 square. I'm open to the idea of expanding the canvas later, but first I'd like to see this challenge through.
Update: