Everything I write below should start by "IMHO" ...
A : The rainbow effect feels weird.
B : An empty plate feels just as weird as what was there before... You should remove the whole plate..
C : I'd like to get at least a little bit of sky reflection in the windshield... Something that makes it fit a bit more with the side windows
D : This highlights feels weird.
E : There's something weird with the ground... This late in the afternoon, the ground should be way more contrasty I think...
Red marks : Just a few visual annoyances I'd get rid of.
I also think you should push the highlights toward a warmer tone... The side of the cars is great, but the top feels like it's lit by something else than a warm late afternoon sky.
In addition to what JK pointed out, I feel that he lighting on the car is not consistent with the darkened sky and clouds you have added. Especially the lighting on the hood of the car. The added sun is a bit off. It's also not consistent with the lighting on the car or the ground behind the car. The car is not producing a long shadow consistent with the low position of the sun.
Just as a side note, even though "lens flares" do happen in real photos, most retouchers get them wrong. They are a dead give away that the photo has been Ps'd.