My visuals wishlist (Assuming this is for the ps4):
Higher resolution textures (Duh)
Volumetric Lighting (Imagine tracks like the ring at early dawn with this
It would really pull the already solid lighting model together)
Higher Quality Shadows WITH FILTERING (The lack of filtering is the biggest thing making them look blocky)
The heat distortion effect from Gt3 returning
Weather and realtime shadows available on all tracks
All "premium" quality cars (Duh XD)
More variety in time.
Particle effects rendered at full resolution.
Higher Antialiasing
60 Fps
Higher polygon count on tracks.
A sense of speed closer to Gt2 (Might not be the most realistic but it is fun)
More "activity" in tracks (IE: Falling leaves, people ducking out of the way like on Grand Canyon in Gt4, ect)
More grass billboards where grass is.
Tessellation (Applied to cars to remove any jagged polygons close up and maybe add extra bits of detail)
A higher quality damage model (The one in GT5 is pretty laughable due to the lack of real change on the vehicle)
Less Zombie Gordon (
http://www.youtube.com/watch?v=_YwbAQn4VXo )
A color pallet closer to that in Gt3 (they had it perfect at that time).