Hi!
An edit:

->

Bullet-points of my thought process behind this'a!

+I'd say the biggest issue with your piece is using black outlines to convey information. It's really harsh harmful to the picture! Using either lighter outlines or good use of planes (surfaces of light)
+His hair. The highlights on his hair are actually quite good

Hair is one of the hardest things to get looking right, so be proud

! There are issues with it though: the way it's shaped makes it look like he got his hair all salon'd up. Straighten it up and remove some volume and he'll be more metal! (his hair is still pretty big in my edit, heh)
+I changed the skintones a little bit. Only thing that really mattered that I changed was upping the saturation of the base tone.
+You're banding a lot of your shading, most visible on both of his shoulders. It's difficult to explain so just see this post by Helm:
link +I made him an amputee because I didn't know what to do with the arm

+Anatomy~!
++ His face: I made it more realistic. I don't know what to really say? lowered his mouth, made his ears a bit more separate from his face, cut out the black lines, made his eyes more implied and his brow more visible.
++ Torso: highlights on his chest are the main culprit behind gender confusion (assuming he's a man) so I flattened it out

Also, the waist going inward is another feminine thing, men are made out of manly flat shapes! You should look at
a reference image for, well, just about anything anatomical, just a quick glance will show you some issues: the 'sixpack' is more spread out and less defined, the chest is higher up, ribs aren't visible on people with six packs generally, so I think you should decide whether you want him underweight or fit. Also, his torso is definitely the weakest part of my edit. Y'know why? because I didn't use a reference

++ His shoulders are slanted, another feminine trait

if you straighten them out and broaden his shoulders, he looks more manly.
Hm, I'm probably forgetting something.