It's depend on what you look
The graphic is amazing the car is fully detail if you compare with other racing game gt5 has the best car model, the circuit graphic is very good, people always complained about bad enviroment graphic but its has feel of real life i mean if you look at trees in gt5 and you said "the trees is very bad", i don't think so, if you put dirt or forza's trees graphic in gt5 it will look cartoonish even it have better render.The circuits graphic are good too, sometimes its have different atmosphere each track.
The most important thing in gt5 is driving physic, don't compare it with forza 3 because gt5 win in every way, if you're looking game for just have fun play forza 3.