The detail of your sketches is quite accurate, but unfortunately the main frame of them (this is the car pictures, the plane ones are nice) is not square, and things like the sizes and shapes of the wheels are a bit poor.
If you set out the main body of the car in better perspective then with the detail they would turn out nice, but as it is they do look all out of proportion. The hummer i'd say is the best car picture you have up. The jet pictures are good, as are some of the character ones.
No offence is meant by my comments, and i hope that you posted your work in order to get usefull critisism rather than praise.
Cheers