The best part of this game is the realism it imparts to the driving experience. The game has a range of cars spanning over 100 years and over 1000 HP (starting at 1 hp). It has tracks ranging from simple to complex monsters (accurately based on the real life Nurburgring in Germany.) Tracks can be tarmac, dirt, ice, snow, wet tarmac and sometimes a mix. It has driving licenses which help you learn to drive better in the game (I've passed them all, but not gotten perfect in more than half...) It has room for 1000 cars in your garage (I'm at about 800) There are plenty of races that are snap easy, medium, or difficult, short or long.
Most cars can be modified by adding suspension, drive-train and engine upgrades.
So there is a lot of variety in this game. You are not stuck driving one of 10 cars or something, though some races restrict your options to one or more cars, but that is just for that race or series of races.
Above all it's the physics that drives this game above the field. A nice selection of cars is nice, but the feel for the road is the best thing this game has for it.... As the car accelerates or decelerates, you can see the car lunge or dip on screen. As the wheels start slipping, you hear it, and if you don't correct it, you might just loose it. As you hit a depression in the road or crest a hill too fast, the tires loose grip a little, and it just might be enough to spill. Just like real racing, the driver must know the road and the car. Knowing and staying in the limits is vital to racing at your full potential.
This game is NOT an arcade game where you just floor the gas and steer. This game requires you to be more subtle than that. As it's not an arcade game, it won't be for everyone. Even those who don't like driving (like me) may really enjoy the game, as you can get the feel of the race, with out the risk (to your life and property...)