The Mario Kart series gets its obligatory DS entry, and Wi-Fi makes all the difference.
The single player 'main game' is simple: do a 4-race cup, and do well enough to unlock further cups, and do so for 3 engine classes. The action is fast and furious, as you fend off 7 challengers, some more of a threat than others. With the chance of an opponent getting a weapon (via one of several arrays of item boxes on each course) to stick it to you over your head, you're kept on your toes the whole time, both avoiding obstacles and doing what you can to defend yourself. And you'll enjoy every minute of it. A Time Trial mode allows to challenge yourself to get the best time possible on a track, and allows you to race against a ghost of your best previous run. A Mission mode has several missions, where you're forced you to complete 8 specific tasks to unlock a final boss. DS to DS wireless multiplayer and Wi-Fi mode pit you against friends or anonymous people across the globe. Up to 8 people can compete locally, or 4 via Nintendo's Wi-Fi network, and competing against people, each of whom can use what they've unlocked, is the game's real thrill.
The sheer thrill of wireless play is the game's strongest asset, giving it high replay value and (via Wi-Fi) a large pool of potential opponents at any hour of the day. While the touch aspect of the DS is only really used for menu navigation, having a separate screen for a map is a very convenient way to keep tabs on the competition.
The one Achilles' heel of the game comes in Wi-Fi, in that finding a balanced match can be frustrating. Even using the Rivals mode, which seeks to match people with similar win/loss stats, it's very easy to come up against an opponent who far outclasses you, which sucks the fun right out the game (and finding you're far better than everyone you're racing against isn't much better). That problem can be mitigated by trading friend codes with people of similar skill levels. People who shut off their systems when they start losing is another plague. In single or multiplayer modes, some sound bytes get a bit repetitive, as you get tired of hearing the same chuckle when an opponent passes you.
The game plays very easy, and the 'easy to learn, tough to master aspect' means anyone can jump in, but you'll still need to dedicate yourself a bit to get all you can from the game. The controls work great, and the most advanced players can really get the most from their power slides. Graphics are exactly what you expect from any Mario game--everyone's recognizable and cartoony, so you feel a part of the Mario universe. Sound is also Marioish, and effects like screeching tires and revving of the engine make for some level of realism. There's near unlimited replay and value, so long as the game remains popular, though as more Wi-Fi titles become available, even dedicated users could stray. The best way I can recommend this game is to admit I'm not a big player of racing games, but I absolutely love this title, and anyone with a DS should buy it.