thing that stands out the most to me is the lighting...it's rather bad. i don't mean to be an ***, but it is, but that could very well be due to the equipment. I would suggest rigging up some ghetto form of an umbrella or some sort of diffuser if you don't want to/have the money for umbrellas.... the lighting is far too harsh. i don't have a lot of experience with lighting, but what i'd do...scour the web for car picks you really like done by pros. then try to mimic what they do. obviously you won't be able to mimic completely because they have far more/better lighting equipment, but still, it's a good way to learn.
i'd also suggest softening the shadows, a lot of them are really harsh, a lot to do with the harsh lighting, but... get some reflectors to fill in those shadows a bit to soften them up. just get a big board or something large and square, and some cheap tin foil and bam you have a reflector
just mess around, i'm sure you'll have fun trying to get different effects with'em.
i'd also try to mess with whitebalance in photoshop as well, try to make the lighting a little more natural look, not like you have the popup flash on'em. it won't take too much adjustment, at least i wouldn't think. but it's WAY easier to adjust it in RAW than it is on the camera lol.
other than that, better cars/location
