I hope you dont mind edits.
I edited one of its leg to illustrate a few points :
The first criticism I want to level is your palette : you're using pure gray, which is the most boring thing on earth.
I think the Ghost in The Shell robots are blue so I used a high saturated blue but even if it was actually "gray", it would reflect some ambient light which ends up bluish on metal (in most cases).
Pure gray = no · Tinted gray = yes
Another of your color mistake is the use of pure black inner outlines. Using black outlines is ok but not inside your sprite, that's a waste of space and aesthetics.
Next one is your shading : you chose top left as your light source and then you gradiently shaded stuff from top left to bottom right.
It's better than pillow shading but you're still thinking flat. You must imagine the whole thing in 3D.
It actually helps me to have in mind a lowpoly image of my pixel art, you just have to shade your virtual polygons in 3D SPACE.
Concerning metal, dithering is its worth ennemy and contrast his best friend. Keep that in mind
Design is not the biggest issue here but I think it looks more pleasant to add details like the segmenting. I also made the three fingers more one like another.
Hope it helped =)
