Wow! This is a really awesome piece of art! I like how the shadows made sense, creating a darker side of this robot. The simplicity of this (not saying it wold be easy to draw, but just how it just focuses on the robot and nothing is really taking my vision away from it) is great!
I feel that maybe you could have added a color for an "eye" in the center of the head, but it works well without it. The rust points on the robot show that it was long forgotten, or has been wandering for many years, collecting that rust throughout life.
I really like this art and would love to see more from you! (Maybe more robots, or trying to show the world that this one lives on.) I think that you will do great in any art that you come up with. I can't wait to see what you put out next!