For starters, they're too short. And they're dull to look at. The tracks cut through generic cities and countrysides that look like the backdrops for countless other racers. Most of us get plenty of dull scenery during our commute. Some might argue that misses the point.
Players get to compete as any one of several characters from the animated series.
More characters get unlocked as players win more rounds. Each has his or her own set of skills and attacks. Barney the drunk, for instance, belches up a foul cloud to knock out his opponents and Groundskeeper Willie hacks his foes with a rake. You get the idea. And, probably, you get enough of the joke that you don't have to buy the game.