When I first heard that Nintendo was offering a free online service it was music to my ears, so naturally I had to pick up the first game that would ever use it. I was able to get a copy of Mario Kart DS the day after it was released, and I still play it occasionally to this day.
The thing about Mario Kart DS that really captures me is not its use of the DS's two screens, nor its graphical quality. What I like is how much immense amounts of replay value there are within this single game. There are four normal cups, each with four tracks; as well as four retro cups featuring tracks from past Mario Kart titles in remastered graphics which also each have four tracks. That's a grand total of 32 tracks in the game, not to mention that you can play them on three difficulty levels (four after completing the third), and that playing them unlocks new karts and characters.
Now, back to the online mode which propels this game's replay value higher than any Mario Kart before it. When you first connect to Nintendo WiFi Connection with this game you are allowed to play with friends or with random people. Of course to play with friends you need Nintendo's cumbersome friend codes, but that's besides the point. You can only do Grand Prix mode online (no battling or time trialing), but it still allows for an extended experience, simply because the players online are so talented that winning is quite a feat. I have to add that for all of its grandeur, this mode does not include every track in the game, cutting out some of the more fun and exciting tracks most likely to save space.
The Battle Mode in Mario Kart DS allows you to play the classic Balloon Battle, or a new mode called Shine Thief, in which you fight your opponents for Shine Sprites (which were introduced to the series in Super Mario Sunshine). Though a similar mode exists in Mario Kart Double Dash for the Gamecube, they are not the same thing, and I honestly prefer the DS's. Both battle modes are lots of fun to play with friends, and for the first time in the series' history, Nintendo has opted to let you play battle mode alone against computers as well.
The last mode in Mario Kart DS that is worth mention is mission mode, which has six levels, each which has a three by three grid of challenges inside. When you complete the eight bordering challenges you can fight a boss who resides in the center square. The challenges can range from defeating an opponent in a race backwards around a track to collecting coins within a time limit. I have yet to complete this difficult mode.
Overall, Mario Kart DS is a fantastic game – by far the best in the series – and I recommend purchasing it if you don't already own it!