Looking for advice more than praise, but don't let that stop you by any means :P
I'm debating on whether to fill this in with black and white pencil shading or colour this bad boy in, whathcu' guys think?
EDIT:
FYI: There's Void energy emanating from his right hand at the bottom of the picture and I'm planning to place a rifle in his left hand which you might be able to see poking out alongside his forearm.
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Why not do both? Scan it, make a few copies, then fill them in as you please with different mediums and different shades. See which you like the most.