hah - as soon as I saw that BG i realized that you worked on Eternity's Child (i've been talking to Luc lately) - although i'm not quite fond of the BGs at all. I love all of the vehicles though - quite awesome, and retro.
I'd suggest you use more dither patterns on the background. Right now your only using two (pure 50% and an in-between) Not quite fond of the colours in the sky either. Maybe I can knock up an edit a little later
-Dan