Not trying to be too picky, but since you asked...
I meant the shape of the rear side window, too. I think the bottom edge needs to follow the contour of the fender arch, not stay straight like the ATS. I also feel that it would look better if the rear side window was made a little smaller. Similar to the 5th gen, but of course there's always a risk of making the car look
too much like a 5th gen. It's a fine line.
While I'm making requests, can you change the chrome border to black?
The hood scoop is too high, that kills a lot of visibility. Would you make a low-profile extractor type hood?
I could go on and on with little details, but I've gotta leave it there so I don't kill
your concept.