I myself won a race in which I flipped over on three, non-consecutive occasions and was even hit by a train. The environment sounds are great. Each part of the track sounds a little different. You can hear the wind blowing through the trees or the gentle murmur of a waterfall. The sounds are all source specific as well.
Car noises are great.
The crashes aren't realistic enough to be disturbing and the various horns and sirens in the game are well designed. Surprisingly, the horns are used fairly often by the computer players. The music is the only thing in the sound department that fails to impress. For me it was pretty much the same thing that all the other racers are doing. Just another techno style soundtrack in my opinion.