I've had a lot of fun with this game, especially with friends.
Now, let's get to the facts: There are 3 modes that you can play this game in.
1. Air Ride Mode. For most people it's the main part of the game. There is eight stadiums you can choose from. One has to be unlocked. You can set the computer anywhere from level 1-9 and you can adjust the handicap. You race, you earn things and use them. You can earn new stadiums, new color Kirbys, and new ships. There is a checklist that gives you tasks to do in Air Ride Mode and by doing these tasks is how you can unlock things. This part of the game is especially fun multi player.
2. Top Ride Mode. This is the mode I had the least fun with. It's a racing mini game except instead of only seeing what's in front of you, you see the whole track the whole time. You can choose from two ships and the computer levels range from 1-5. Some laps on some courses on top ride mode can take less than 4 and a half seconds. Again there is a check list and by completing things on the checklist you can get different color Kirbys.
3. City Trial Mode. This is the mode that I had the most fun with. In this game all players start with the same ship and look around the city for more ships and different power ups. The computer levels and handicaps are the same as Air Ride Mode. The point of looking for power ups and better ships is for the challenge after the city trial mode is finished. The power ups that you can find are top speed (your top speed gets higher), offense (the offense of your ship goes up), HP (the Heart Points of your ship goes up), defense (the defense of your ship goes up), boost (your ship gets a better boost), charge (your ship gets a better charge), turn (makes it easier to turn your ship), weight (self explanatory), and glide (makes your ship fly farther). You also look around the city for a new ship for the challenge.
City trial mode is really competitive and really fun and we always have blasts playing it for hours and hours at a time.
There is also a LAN mode on Kirby Air Ride that I haven't looked into yet.