There is something horribly wrong with this game.
Mario kart's story begins in a far off -- wait, no. Mario Kart is completely devoid of any story. But who cares? If you've never played a Mario Kart game before (In other words, if you've been living under a rock for the past few years), the objective of the game is to select a character from the Mario universe with which to kick the asses of other characters from the Mario universe in an intense kart race involving various items, such as green shells (used as projectiles to... eliminate the competition), banana peels, and mushrooms. You begin with 9 characters, with two karts each (this doesn't last long...), each with varying stats, such as drift, acceleration, and top speed.
Veterans of the Mario Kart series will notice some simillarities and differences. The drifting concept carried throughout the Mario Kart series is ever-previllant here, and functions the same way as it did in Mario Kart: Double Dash!! for Gamecube. A new mechanic that you'll discover very quickly, though, is the concept of drafting, ripped straight out of real-world racing. You will gain a substantial speed boost simply by driving in the slipstream of a player behind you. Although this sounds good in theory, this generally becomes the cause of much frustration when repetitive passing ordeals are held until someone finally decides to give up. Backpedaling slightly from MK:DD!!, all items are once again available to all characters, but a newly-implimented item stat detirmes how good the items you get will be. Of course, the usual Mario Kart ballance is here (the further back in the race you are, the better items you will get). Also added are two new items: The bullet bill, an item that will cause you to fly forward along the course at a blinding pace for five seconds, and the blooper, which will cover the screens of all opponents in front of you with black ink, and cause AI opponents to swerve for the duration. These items are integrated seemlessly with the existing items, and nothing feels out of place.
The 16 new tracks in the game (there are 16 others taken from the various other games and slighly modified) are, for the most part, well designed and well-detailed. The retro tracks, however, seem to be lacking polish, and some have removed shortcuts and some simply look like crap. Other then that, the courses are a blast to play on, especially in the multiplayer modes.
The multiplayer mode is extremely limited. Parts of it are badly designed. Due to Nintendo's extreme parental care ideals, you will probably never play the same person twice. Despite all this, the multiplayer is what will keep you coming back. Why? Just because.
Overall, Mario Kart DS is a crown achievement on the DS, and if you own a DS, I'd highly recommend buying it.