hey whaabamb, these are looking good! i agree with christian about the lighting, but its nothing a directional light and some quicky Light Tracer wouldn't fix.
Also, on your Tatooine shot, that transparent atmosphere should be glowing blue, don't you think?
http://en.wikipedia.org/wiki/Tatooine
This whole thing seems to be kinda having a cartoony type feel, which is really cool! your blockade runner kinda looks "plumpy", if that makes sense. Looks great!
and fire coming out the back? maybe some glowing blue gas fire looking stuff, of maybe just a blueish white glow... I don't know how accurate you want to make it.