GT5 prologue has amazing graphics, the final version will probably mainly include many new cars and tracks, but the game engine will advance as well and should include stuff like car damage, prologue may see such updates as well through downloadable enhancements as the developing company stated they are nearly done negotiating this addition with the car manufacturers.
Overall graphically I think there's not that much need for improvements, the cars look absolutely breathtakenly realistic, much better than anything we have ever seen in a realistic driving game ever before, some tracks can have a bit more polish, more special effects and such.







