Doesn't look turtley enough.
Don't give up. I've had all my art to date failed.
It's awaiting revision still due to the lack of positive votes via the public queue. You have a lot of banding on this piece. Also, make the background transparent as it serves no purpose (As stated in the rules).
Why is my art still waiting for approval, its been almost 3 days
I want to come up with a collection of various isometric vehicles. Next one will most likely be the ghost buster mobile
Try adding some dimension to the spare(circular shell on the front of the truck). Needs more seperation between the tires and the van. Also maybe try a slight hump in the roof to add some style more akin to a turtle shell.