I beat Crash Nitro Kart on the Nintendo Gamecube. I unlocked all 8 hidden racers, unlocked Hyper Spaceway, and finished Adventure Mode 100% with both Team Bandicoot and Team Cortex. The last one was very tough because I had to unravel and beat all of the N.Tropy phantoms in Race Time Trial mode.
Just in case you didn't know, Crash Nitro Kart plays just like Mario Kart, but with a more detailed and advanced boosting system, upgradeable weapons, and anti-gravity driving. F-ZERO X and F-ZERO GX already had anti-gravity driving, but the kart racing genre never had anti-gravity until Crash Nitro Kart. How CNK does anti-gravity driving is that whenever approaching gravity roads, the tires spin sideways to take effect of the gravity. The tires go back to spinning upright if the road has no gravity physics.