Depends on where you look.
Compared to other racing games, I notice that Gran Turismo has a lot more detail (and therefore, processing resources) going into the cars rather than the surrounding terrain. That's why all the "GT6 graphics are terrible!" screenshots focus on off-track terrain or standard cars. All the premium models look lovely, and not just in Photo Mode, either.
Also, Gran Turismo 6 has dynamic weather and time-of-day lighting, something which is extremely taxing on the PS3's limited hardware, hence why every other racing game with dynamic lighting/weather (Driveclub, Project Cars, etc) are all on 8th-gen consoles.
"Never argue with stupid people. They will drag you down to their level and then beat you with experience."
-Samuel Clemens
