This is the kind of game that makes you want to cancel your Gamefly account. I wasted my first Q on this game and now I have to wait a few days to get another game. If you want to try it out, go rent it somewhere, that way you can return it asap after you find out how bad it sucks.
If I could only have one DS game, there is no doubt in my mind (as of today's date) that I would choose Mario Kart DS. The series finally got back to the true racer form of the original. That is: anybody can play and enjoy this game, but you can never master it.
Gone is the rubber-banding from Mario Kart 64. (players not in first place go faster than the leader)
Gone are the more open courses and unbalanced special items from Mario Kart: Double Dash. You are now on a real track bumping other players rather than just having a power slide competition down DK mountain.
Included are two new features that add multiple dimensions of gameplay. First, you can see every player's items. Second, you can get a speed boost by drafting behind an opponent. What makes these features so great you ask?
When you are leading the pack you have two goals: to go as fast as possible, and to keep second place off your tail. Otherwise, he can draft behind you and take the lead. Additionally, (if you are good) you can see when a blue shell is coming and slide into second place to avoid it. There is so much more to be aware of during the game. It used to be you got an item and you used it in preparation for the next item. You went around the course the same way every lap. The addition of drafting and item visibility allows you to make more strategic decisions as you race.
The point is: the winner of the race is no longer as random as before. The sign of a great multiplayer game is levels of gameplay that keep getting discovered as you get better. For example, Halo and Street Fighter 2 both have this quality. If you are on a higher level than your opponent, you will dominate them. The same is true for Mario Kart DS.
The only thing keeping the rating from perfect is that the Wi-Fi isn't as fleshed out as it could be. I would rather see some better match-making and community features a-la Halo 2 or Warcraft 3.