My only suggestion moving forward is to try some different colors, textures or 'treatments' on different parts. Something like the gun being a different color than the car...or the armor different than the fuel tanks.
I see you wanted an overall rusty look, and that's cool. Just a suggestion for the next go round.
See your point Scott. I was experimenting with the AK Red Modulation set of 6 different shades. It was my first time with an air brush, so it didn't quite turn out as I would have liked it. There isn't enough color separation :-\ Hopefully, the next one will be better.