Atrocious? Please. I'd call the soundtrack zany or corny, but I wouldn't call it atrocious, especially since it fits the surrealistically zany settings in the game. I mean, you're racing in seemingly real-life rural settings, on transforming vehicles that resemble various robotic critters, racking up those stars by pulling off stunts like doing 360 degree turns in the air, hitting baseballs, swinging on bars, rescuing butterflies, throwing pies at clowns' faces, and playing the tambourine.
With that in mind, I think that the soundtrack fits nicely, though there are a few tracks that I think are awesome, such as the Title Theme, Replay Theme, and the track themes for Fiji, Guatemala, Finland, Egypt, China, and Nebula.
Edit: Oh, and in case anyone is looking for a playlist to rip, YouTube member MatzeSuperMario has the soundtrack up on YouTube. The soundtrack can be found on the following playlist:
http://www.youtube.com/view_play_list?p=11E0344379E847A6