I am a racing fan and usually prefer Simulation type racing games like Forza.
I decided to give SHIFT2 a go by renting it, not expecting much, but am pleasantly surprised.
Put simply so as not to write an essay, this game is most definitely NOT a sim racer. The handling is completely unrealistic, with cars CONSTANTLY sliding no matter what you do. This is most profound if you like using the rear chase view; it looks terrible and is impossible to use as the car literally jumps around in a jerky and totally unreal way.
It is however, HUGE fun, providing you switch to bonnet/in-car camera views. This is because, when you accept it is still an arcade racer in realistic life-like clothing, you can enjoy the fact that the handling is v.good fun (takes me back to RidgeRacer/Sega Rally arcade units) and that the racing is close and enhanced with an excellent sensation of speed.
My advice is, if you want a fun racer, you HAVE to get this.
If you are unconvinced because you usually like sim racers, live a little, accept that this isn't one and enjoy it.