Likely the Best Mario Kart Thus Far
The game is basic MK greatness. Choose your driver (they all have an additional car now), choose your speed class, and go racing! The lower level classes aren't all that challenging, but the computer AI steps it up in the higher classes (which equals a bit of speed boosting for them if you are ahead, as is usual for racing games). You can hold one item at a time to use against your rivals from the classic green and red shells to Bullet Bill powerups. Part of the gameplay mechanics also include 'drafting' to get a speed boost and the power sliding boost featured in the gamecube version.
Winning championships unlocks a few new drivers, a nice feature to keep it interesting.
The wi-fi connectivity is a great feature...one I unfortunately haven't been able to delve into yet. No wi-fi for your internet? Use the nintendo USB-wifi connector for the DS and you'll be ready in no time.
Admittedly, the controls can get a bit uncomfortable on the DS. This is made easier on the DS-Lite, plus you can always modify the control scheme to your liking.
Mario Kart DS is deffinately a great game and a hallmark in the series. Although there isn't anything ground breaking here as far as changes to the series, it is more of the greatness that made the others so much fun with many modes and options thrown into a handheld package with wireless functionality. Go get racing!