It Is A Start...
One of the biggest things I have a issue with this is the lack of clarity. Everything seems kind of blurry and having any sort of real solid definition. The joints, the contour, parts of the background, they all seem to lack anything that really reinforces the figure or piece in general.
I think you should go back and give this more contour. It would also be a good chance to give this a stronger metallic feel. The arm could use more of a metal feel by adding a array of lights and a darks along the length of the arms and head to re enforce the material.
Take a moment and look at these pictures of metals and how they reflect and surroundings;
http://www.etftrends.com/wp-content/uploads/2010/05/Stainless_Steel_Pipe.jpg
http://www.artlex.com/ArtLex/s/images/steel_kapoor.turning.lg.jpg
http://image.made-in-china.com/4f0j00qBSacpbrJEog/Stainless-Steel-Tube-2.jpg
Now your robot doesn't have to have mirror quality reflections, but more of the basic lights and shadows worked and formed steel tends to put off.
One thing I do enjoy about more the majority of the piece is the lighting. if it wasn't a robot made of metal, but a normal human then the light play would be pretty good. you have done a pretty good shadow cast except for a few areas.
One of those areas is the reflection in the mirror. the hand above the eye cast a shadow straight down. the lighting on the rest of the robot suggest that the light source is not exactly above, but a little more to the right and a little closer to the mirror. Although this isn't a perfect shadow, it does serve a purpose for the piece which I guess is a good enough excuse.
I Kind of enjoy the blue lighting on the back of the head but it lacks a source. I'm assuming that you want the source to be in the head, but at the moment the only thing that would make sense is that their was an independent light off the scene projecting on to the robot, but that doesn't work either because then the light would be projected on more than what it is. I thin you should get something in the scene, particularly in the head to have a source for this blue light. Also on the robots left hand the blue light has a strong hit on the top of two of it's fingers. the only way for their to be a light that strong on that side would be if you had a light at a completely different angle, so you may want to correct that.
One of the last things I want to point out is the yellow sparks. They seem so out of place and have no real reason to be there. I think if you want them coming from wires, which I think you do since I can see some wires starting to lead there, then you should get some fraying to those ends. This will give you some opportunity to have some more fun with some unique lighting.
At the moment, I think you have a start, but it is kind of shaky. You need to go back and make some corrections so people have a much better idea of what this bot is made of, as well as its form. The more defined and cleaned up you make this the better it'll look.
Good luck, if you choose to make any changes, take them one at a time and it will lesson the work load.
I will look forward to seeing some improvement in your future pieces.