not bad for your first ones. I'm a graphic designer and I use photoshop every day, so I can attest to the difficulty of making these look perfectly realistic. All I can say though, is that attention to detail is everything. If you cut corners or don't take enough time, then it will be obvious.
Take for example the curves of the wheel wells, especially evident on the Camry and sti. the cutout lines are jagged and not smooth. Keep up the good work, but keep in mind that the little things are what will set you apart.