Sound effects are superb. Engines whine and roar in convincing fashion. The audio also varies dramatically depending upon what you're currently trying to pull off. Leave the roadway and you're rewarded with the frightening sound of tires whirring helplessly in mid-air. Steve McQueen wannabes take note.
Atmospheric effects are also very nice.
Take a curve too fast and your tires will scream at you to slow down. Wind howls around your car as you navigate narrow cliffside roads. Horses whinny and birds chirp while you roar down shady country laneways. Rain hits your windshield with a realistic splat. Another great audio touch is the ability to play your own music CDs while racing.