Hey Skuttling, The lines/shapes are good, so I didn't change too much there... The rendering had the most room for improvement.
I had fun doing this.
These are the things I did, In the following order.
First, to reinforce the lighting, I added a gradient(orange-dark blue) in overlay mode on a new layer.
Then I added rim lighting on the clothes, to help separate the characters, and to be consistent with the lighting you had on the arm/face.
Darker shadow on the middle ones face, subsurface scattering for his ear also.
Repainted the cloth for the guy in front. look at old masters like Alma Tadema, John Singer Sargent, etc. (do studies!)
More contrast for the one in front, More light for the wrinkles/folds in his skin.
Shifted his head up and his shoulder down, for a more natural pose.
I wasn't sure about the blue/darker patches of skin.(looked a little like 5'o clock shadow :P) So I added the stripes on his head to lessen confusion.
To play with saturation, I filled a new layer with black on color mode. Erasing into it and changing the opacity to get the look I want.
In the background, in the upper left corner, It looked vaguely like a city. So I painted more across the image, while removing the beams of light.
Light haze between characters for separation and atmosphere.
Redone light beams, more subtle.
I softened the edges in the shadows, less contrast between the background so the focus remains on the lit faces etc.
Hope this helps you.
Edit: After looking again, I felt the yellow light in my paintover was off.. I've added a slightly modified version.