Gt is hardly a simulator. Sure, in some ways it is, but in most ways its dumbed down to be accessible.
Still, its a fun game. Driving an Alfa Romeo Spider in GT4 around that one Italian track was honestly one of the funnest things I've ever done in a game. Of course nostalgia played a heavy role in that....
Graphically, the car models are probably tops. But the environments are lacking, and the crowds animations look terrible in motion.