This is terrific. I like the concept of a sci-fi samurai/ronin that's not overly fanciful, not too fantasy-leaning.
My only criticisms are: (1) his feet look a little small, (2) the design of the helmet has so many varied angles that it's unclear if the drafting/perspective of the helmet is a little bit off, or if that's just a side effect of the multi-faceted structure, and (3) it seems a shame this is fully monochromatic; I'd love to see this design in various color schemes.
Also, while I enjoy the asymmetry of the design, I find myself wanting to see what the right shoulder pad and forearm guard look like. Providing a detail of those two parts would rock. But man, overall this is a superb piece of work!