It seems to me that you're aiming to a comic book style inking...so here's a couple of thoughts: I was comparing your inking to alvin lee's work and there seems to be a lack of interpretation of the lines of the penciller; he uses different kind of lines to create rhythm and convey different meanings; for instance, the lines in the shoulder pad are thin and clean, because he's trying to communicate that it is perhaps a metal shoulder pad, whereas in yours the lines are wobly or insecure, thus the shoulder pad looks like it is made of wood or another softer substance. The same thing happens where you hace a bone, you'd want to use lines that are straighter and bolder. Another point that came to my attention is line weight; you may want to use wider lines for things that are closer to the viewer so as to make them look closer; there's little variation on the width of your lines in the cases of the hand/feet close to the viewer and the ones that are farther away, thus making the image look kinda flat.
One more thing, if you don't fell confident enough to use black fill try at least doing some crosshatching, that grey you used tends to make thing look softer rather that strong/hard.
I really hope this helps, mate and i love your work :D