The physics are as realistic as those in X-Plane, with engine power, tire cohesion, and aerodynamic drag and downforce all accurately modeled.
The tracks are the most fantastic things I could dream up... tracks that... COULD exist.
Now, with 500+ horsepower supercars and realistic physics, you can tackle those tracks that only exist in our imagination, but COULD be built in reality if we ever dared...
And, with in iPhone 6+ and a cheap Google Cardboard headset, you can do the whole thing in 3-D VR... which is really quite amazing. The world looks HUGE in there!