It's pillow shaded (meaning that the light source is coming from behind the viewer, which is impossible), so i'd say move the shading off to one side. also, this is just imo, but i think the colors should be less saturated if its supposed to be metal. maybe hueshift a bit towards purple when it gets darker (and yellow when it gets lighter) for the red palette and purple and light blue for the grey one? also, i think you should add some more odds and ends on it, like wires, metal plates, windows, guns, stuff like that. A little grime here and there would go a ways. here's and example of what I mean:
(didnt do the top wing things because i have to go)
I'm not really that good yet, but i hope that that helps you a bit (just added 1 color, white. btw, try and use white as much as possible, it adds extra pop to the piece.)