His left leg (our right) seems a bit un natural because it doesn't move at all, also like said above the shirt waves. And also on his left leg at the bottom there is a part you missed shading.
I didn't know you visited here. Glad to see you do for it will help you more than at piccetas.
The colours seem a bit too dull to be metal, perhaps try to give it more of a shine, and some brown as rust? Also the butt area seems a little odd and the legs don't match it. The arm things seem a bit too stiff, even for a robot and the head looks kind of small.
He kind of reminds me of Jean-Luc Picard from Star Trek. On another note it looks alright, he seems a bit out of proportion and the shades should be more noticable on his shirt because it almost looks as if it is a solid colour. And you really don't need 16 colours for a piece that looks like it could be done in probably 10.