♪ I see trees of green, red Mazdas too... ♪
Trees. We see trees while we're racing.
Treeeees!
On the ground, grass and foliage are the only things I can think of that need improvement; the cars are virtually flawless (at the right LoD), the roads are quite roady, humans are good enough, the trees and grass are the only things that really look out of place.
Looking up to the top half of the screen, GTS had many nice skyboxes, and many that looked 'dirty' (Bathurst noon), as well as a few with obvious seams (cloudy Sardegna). Now we're returning to dynamic skies, and more dynamic than on PS3, with cloud formation and stuff. I'm being serious, improvements to the sky will massively improve qualitative assessments of how the game looks, that and better global illumination (or at least better management of contrast in a dark car with a bright sun.)
The comparison I'm waiting to see is how the night sky looks, whether we'll get the amazing views of the Milky Way that GT6 had, usually only afforded by dark sky parks, or if they'll tone it down in the interest of having realistic light pollution (hope not, but anything would be better than GT Sport's few starless night skyboxes where the moon looks like a smudge.)