Well it's a great game! Fun to drive. I've already got the R10 right at the start so I was able to test already one of the biggest cars.
Physics of road cars seems very realistic, with great sounds ( great improvement, especially for the premium road cars ) but sounds of racing cars doesn't sound great at all ( well like all the GT ).
Contact between cars are improved too, now I'm sent into a spin each time a car hit me from the 3/4 rear of my car.
But there is some bugs or some things that are annoying: sometimes, when I launch the game, I can't choose any mode, arcade or GT. So I have to reboot it.
The NSX GT500 ( I've got it too right at the start ) have a funny bug: the dashboard shows you the wrong gear, when you're actually in 3rd for example, the dashboard shows you are in 2nd gear!
With some european cars ( except British ones ), you drive from the right side of the car. Of course in Japan, you drive in the right side of the car, but, when I drive the Peugeot 207 for example, I was surprised to be on the right side instead of the left side, whereas when I drive the Renault Megane, I'm on the left side. It's not a bug, I don't think it annoys a lot of people, but it surprised me.
The standard cars, even if they came from GT4, looks very well on GT5! Of course we can see sometimes a not High Quality textures, but it's very well rendered!
Great game! But if you search a realistic sim, then some rFactor mods, GTR or iRacing ( never test it but everyone says it's the best ^^ ) are miles ahead!