Two characters! Three shadings!
(http://www.davelgil.com/ags/amos1.gif)
(http://www.davelgil.com/ags/amos2.gif)
(http://www.davelgil.com/ags/joe.gif)
I am reasonably happy with the old man's shading, but there is always room for improvement. The younger man I am not happy with at all. Everything I added to his lower face just looked painted on. Any help is, as always, appreciated!
The best advice I can give you is make the lighting on the portraits consistent with each other. It may not be realistic, but when the main character talks to someone and the shadows/lighting of both portraits are completely different it detracts. Try using one you are happy with and making the rest of the portraits conform to it. Here are edits that create pretty much a consistent lighting style. Both are lit from top down and joe seemed to be tilting his head downward to me so I lit him that way.
(http://members.cox.net/progzmax/amos2.gif)
(http://members.cox.net/progzmax/joe.gif)
The top shading for the old man is good. The second, is not so good.
Here's my take on this:
(http://www.2dadventure.com/ags/pissedoffdudepng.PNG)
I guess I'm in the minority, then, if I say that I really like the original shading of the younger guy, and prefer it to either of the edits. The lighting on the forehead and nose only is very simple, but effective. There's no doubt that he has his head tilted down, and his face in shadow. It's my favorite out of all the portraits you've posted so far.
But one thing that ProgZ's definitely has that Dave might want to think about is highlights on the hair. If the light source is above, then wouldn't it make sense for there to be some? Otherwise, the light hitting the forehead, especially right below the hairline, seems weird to me.