I've seen a lot of your art pieces lately, but this one, personally, is the most well rounded. Not only is it well thought out, demonstrated by the additional text, but it is also well executed.
From the ground up, the line art is exceptionally clean and crisp, giving us the definite shape you were aiming for without making us guess.
Next, the colors are well included; close enough in hue to keep the mood you wanted, but separate enough to not just blend into a smear.
The lighting is right on par with what I would expect for a moon being the only light source, but that's not saying it was an easy task.
The only current improvement I could see is to add texture to your robots or scenes. That would be probably the most difficult, but I think the last touch would push your next series of work into masterpiece status.