I'm not actually super-good at photoshop or lighting or anything myself, but I do think I need to mention that one of the problems I see with your shading is that it's muddy. Your tones are mixed up a bit and don't seem to progress entirely smoothly from dark to light on the larger areas - places like the folds in the cloth on his neck look much better than his back. If you don't mind me asking, what exactly is your process for shading?
The way I do it is like I would for my miniature painting. I start with one base color, then for each level of highlighting I make a new layer and slowly work up in brightness.
The back does look weird, I’ll agree! The thing is, his back (Kamen Rider Black’s that is) is made of like a leathery, dull material in the show. His shoulders are like a super shiny black plastic so I wanted to make them stand out more. But his chest/back armor is duller/flatter. I tried to show that through the dulled shading but I messed up, I guess, haha :D
