I picked up a copy of Mario Kart DS this weekend and I must say its quite good. It takes the old elements from the original SNES version of the game, combines it with the fun from the 64 and GC versions and puts it all in one. The addition of the touch screen map is a nice feature.
Not only does it add some new features like the Nintendo Wi-Fi play, but single player has some unlockable missions you can complete. Even though I have completed them, I'm obsessed with getting the best possible scores that I can.
Good job, Nintendo. You put out yet another addiction of a game and my DS is actually getting played for longer than 10 minutes. If anyone wants to get an online game going, let me know. I've been practicing.