I must first say that I am not a fan of racing games to begin with but I still enjoyed a lot of them.
In this case, I give GT5 a 7.9/10.
Graphics were a total turn off. I expect at least decent graphics from a racing simulator otherwise what is it trying to simulate? Even Dirt 2 had better graphics. I'm usually not so picky on graphics but GT5 had some really annoying problems.