George,
I'll happily add some constructive criticism. You're using a different medium than me, so take anything I say with a grain of salt. (Are you using Illustrator or Photoshop?)
It looks like you're off to a pretty good start, but the first thing that jumped out at me was the perspective of the picture. It's pretty inconsistent throughout, which takes away from the realism. Your work paths could be a lot more fluid as well. There seem to be a lot of sharp edges (i.e. around the edge of the windshield.)
Also, the tan insert on the rear quarter looks off center with the rest of the car. It seems to almost be above the side trim.
I'll take another look at it in the morning and see if I can offer up any more advice.
Kris