Firstly my advice is to use preview shadows while using matcap materials if you want accurate models. Also i mainly use basic materials while i'm working. It gives more control, imho.
To being accurate don't forget to activate perspective camera if you didn't. A value between 80-100 is ideal.
And some critiques about your model.
The main proportions looks good. The neck looks too much wide on front and back views. You should check some front photos of this type of male to correct this. Also eyelids need more work.
Just started playing with ZB3 so I am very greatful for the additional comments. I was getting frustrated with the shadows. I think I do have it on the render type preview. It doesn't seem to look the same though as it first did before I played around with the render features. I must have done something. Maybe it will go back to the same when I open it up again. The guy looks way better in my opinion when I was sculpting him. lol Those eyelids have been giving me problems. I had just reworked them before I posted good to know they need more work which I don't doubt at all. I was working without a photo reference but I am thinking about using a photo reference here very soon I am just trying to decide who to use as my reference. I was thinking of doing Vin Diesel but I am having a hard time getting good pictures of him.
Here are the perspective camera and shading corrections that you suggested. It went back to the standard shading setup that I had when I was sculpting. I like it so much better. Thanks for the info on the perspective camera. I looked at the eye lids some more and they need a lot of work. I have not had a chance to work on them and the neck yet.
Does this neck and eye lids look fixed to you? I realised when I was fixing them that this was not my newest model for the head when I decided to redo the model. The prior one had the neck tappered in along with the eyelids fixed. I also detailed the neck up a good bit more. So I guess another question I have for everyone is should I detail out the muscles in the neck or should I leave the neck as is?
This was the Previous Head that I did: Here you can see a more defined neck
I tried redoing the eye region today but it did not go well. I am going to have to take another shot at it. At least I did manage to make the foot look better.
Here is some updates to the eye regions along with the lips and the nasal lavial fold. I am not sure if this is exactly what you were looking for. I am wondering if the regions around the base of the eye lids need to be recessed further.
Sorry I didn't respond sooner I got pulled away on other projects. The armor is a WIP and here is the unfinished forearm armor. I am really enjoying the new brushes in ZBrush 3.1, and I am still adjusting to using them. I am already getting ideas of some custom brushes I would like to make. I have been looking over Giger's work trying to see how he went about his workflow. I absolutely love his work. I hope you like the update. Comments and Crits always welcome.