I have issues with the game, but as far as Wii titles go it is one of the best.
The course selection is fantastic, and putting bikes in the game adds a layer of strategy to it. Being able to have 4 people participate in a Grand Prix and still having a full compliment of CPU controlled racers is also a key feature of the game.
However, the battle modes in this game really seemed to suffer, perhaps due to the courses available to battle on. The wii-mote/steering wheel peripheral for the game isn't an option if you're concerned with winning, the GC controller is far more precise and responsive. There's also really no point in buying this game if you plan on playing it predominantly by yourself. With friends, the "randomness" of the game that you simply can't account for or control in any way creates a lot of welcome mayhem that you and your friends can use to taunt, humiliate, or infuriate each other. Against the CPU's, it's just annoying.