Female Head Model

I've decided to start posting up the work in progress shots from a female head model I made a little while back and analyse/evaluate the model. My brief for this female head was to create a highly detailed model based on some reference photos. She also would have to be bald/have a shaven head, which sounds easy, just don't model hair. But it can be quite tricky to make sure the shapes of the head that are normally obscured look right.
I started quite typically with an established head base mesh, the one from my previous male head sculpt, I then used some 3d.sk reference shoot photos as reference for my to push and pull verts until it pretty much matched the reference. The problem with using reference images as a guide is even good reference shots don't line up and whilst you can use photoshop to scale and rotate the images so that the major landmarks match up you are still dealing with perspective distortion etc. So I like to follow the images as much as possible then get the model over into zbrush sharpish where I can very easily use the move brush to tweak forms.
This image above was how the head as looking leaving Maya, it looks rather strange, which is the result of problems with reference images and also working on half the model then mirroring. When you only work on one visible half it often doesn't look right when its mirrored. I set about correcting some of the shapes until I got to the image below, which is a massive improvement although theres still a lot left to get right in secondary forms before I begin to detail. I posed the mouth more neutrally, and need to construct the inside of the mouth before I begin fixing the lips. The eyes need a lot of work but they are at least placed correctly in the head which is almost half the battle.

This image is of the head a bit further along the process, I have altered some of the profile shape of the nose and sculpted the ear to match the reference which is helping a lot, I've also softened the line of the jaw which is making the sculpt read as more feminine. When drawing the female form it's important to use lots of soft lines and only draw lines/shadows based on the light source thus limiting the lines on the face. These things are much harder to do in 3D. I still need to get the balance of detail right to make sure she doesn't look plastic and smooth but at the same time excessive detailing can very quickly age a character.