Pros: Pretty fun, lots to do like missions & whatnot.
Cons: That music is killing me. Just turn down the volume.
The bottom line: Excellent game, excellent graphics, very fun, will bring hours of amusement. Sometimes music can be annoying, though.
Mario Kart DS is a pretty good game. It has different modes that you can choose, a bundle of unlockables and everything.

First of all, there is the Grand Prix mode. There are about eight cups that you can win, half of them are featuring old tracks from other Mario Kart games; for example, Super Circuit for Game Boy Advance; all bundled into this new game.

Then, there is the Time Trial mode. Here you can race by yourself (beat the clock) and try to raise your high score. You don't ride full tracks at once here, you just pick which track from a particular cup that you want to ride on.

VS mode. Here you can race the CPU and there are many options that you can choose from. You can race a series of races, whether you want them in random order, or you want to choose each time or if you want them to go in the order that they originally were in. I prefer random, it gives you a few surprises here and there. You can also choose whether or not to have teams. With teams, all of your team's scores in the race are added up and that makes the total team score. There is usually the blue team and the red team, and you get put on one of them. If you don't want to play in teams, all of the scores are done individually so you'll have to beat all of the other racers to get in first place in the end.

I love the missions mode. You start off at the first level of missions, which brings to you a menu with some missions that you must complete to get to the boss mission and then to the next level. Some of the missions include, power sliding so many times in a particular track, using stars to run into things, throwing those turtle shells at the mole things, and getting through all of the checkpoints in a particular track. There are many more missions, those are just some examples I wanted to give, so you can get an idea.

Another mode is named battle, where you can choose either balloon battle where you must burst your opponents' balloons with items, and try to keep yours save or shine runners, where you have to collect more shines than anyone else, and you can try to throw items at other racers to get there shines. Watch out, racers will less shines get booted over time.

The players you can choose from are Mario, Luigi, Peach, Yoshi, Toad, Donkey Kong, Wario, Bowser and other ones can be unlocked later in the game.

The game is relatively easy, depending on whether you choose 50cc, 100cc, or 150cc. I prefer 50cc if you want an easy ride, but you can unlock all of the levels in each version.

Sometimes the music can get a little disturbing, but that is probably just because I'm a volume off gamer anyway.

Overall, it is a fun game and I recommend it to anyone that likes Mario and/or likes racing.

I have never done any online play, so I cannot comment on that but I have done wireless with friends that were near me and it only allowed me to do the first 2 cups in the regular mode and first 2 cups in the retro mode. It was pretty fun though, but it appears that the second player, the one that uses DS Download Play, cannot choose their racer.