Positives:
# Mario Kart DS enables two, three, or four player races in 20 of the available 32 race tracks. The match-ups don't feature computer opponent drones, and the more active tracks with tons of environmental hazards (like giant rolling balls) have been taken out of the equation. Battle Mode is not an option.
# Mario Kart DS has the ability to keep a log of people you consider friends. These "friends" are obtained two ways. 1) Playing people in local wireless multiplayer (i.e. in the same room, connected system to system via the standard wireless protocol and NOT the Nintendo Wi-Fi Connection) will automatically transmit that person's ID into your Friend's List. 2) Each player's game has a unique 12 digit "Friend's Code." You can give that code to your friends, who can enter it into their own game with a temporary name. When logging onto the Wi-Fi Connection with the DS, when the DS sees that person online, it will automatically pull the appropriate user name and his icon. The temporary user name that you entered will be overwritten in favor of the data that the other user has already registered. And Friends can be removed from your list easily.
# Mario Kart DS automatically links players together in the match-up. By choosing "Friends", Nintendo's server will go out and pull players on your Friends List also sitting on the Connect screen waiting for a match-up. "Rivals," in theory, pairs up players with like-skills, most likely comparing the wins/loss record ratio. Regional matches up people in the same territory, and Worldwide connects anyone on the planet together. Worldwide runs the most risk of lag, since you could theoretically be playing people from Japan, US, Europe all at the same time.
# Mario Kart DS keeps track of the win-loss record against members in your Friend's List. If you want to see how many times you beat that Friend, that data is recorded to cartridge so you can take that data with you to gloat (or hide). Unfortunately, it doesn't keep track of your wins/loss records against players that aren't listed as Friends on your cartridge...and currently, the website doesn't offer this data, either.
# Mario Kart DS will alert you when a Friend is logged on and waiting to play a match. Right above the Wireless strength bar, a blue "Friend" icon will pop up and blink when he logs onto the Wi-Fi Connection with Mario Kart DS. This icon pops up anywhere: menu selections or in-game during a race. Unfortunately, players can't see which friend it is, nor can they interact with them in any way. It's just an alert, nothing more.
And now, for the negatives:
# Mario Kart DS online racing is a little more limited. Certain elements have been tweaked or removed to make the game run as seamlessly as possible. The "Three Banana" power-up has been taken out of the equation, and players can't hold a banana peel or turtle shell behind their kart for protection.
# Mario Kart DS does not allow for specific match-ups. Let's say I want to play my friend MrKori and only MrKori in a one-on-one race. The only way I can do that is if I make sure that he's the ONLY person on my Friend's List (meaning, I've physically deleted everyone else), and he's logged on and searching at the same time under the "Friends" search setting. You also can't force a two or three player race. The server will automatically give up and let two or three players race if it can't find a third or fourth player to match up, but players don't have the option to go ahead without the additional racers.
# Mario Kart DS does not allow players to "Friend" online racers. If I play a Regional or Worldwide race, I'll be playing against people I've never met. If I had a great time playing against, say, ShellBoy, there's no way I can add ShellBoy to my Friend's List because the game never gives me that option. And without any sort of contact information transmitted, there's no way to get in touch with ShellBoy to send him my Friend Code. In theory players will be able to search for names on the NintendoWiFi.com website, but at this time there's no contact info attached to them.
# Mario Kart DS does not penalize players who disconnect in the middle of the match. I've had certain instances where players will power off their system in the middle of a circuit, on the last race simply because they didn't have enough points to push them over the edge for the first place win. If it's a three or four player race, the dropped player will just disappear and let the other two or three players race, but if it's a one-on-one race, that dropped player will sever the connection and all that racing progress will be lost without any sort of mark on your win-loss record.
# Mario Kart DS doesn't pull up the opposing players' overall Win-Loss record unless you're actually racing against them. Your Friends' List shows what your win-loss record is against each player, but you can't see what his or her global Win-Loss ranking is in-game. This may be something that will pop up on the NintendoWiFi.com website, but so far, it's not an option.
At the very least, Mario Kart DS's online interface is extremely elegant in its simplicity, but that simplicity comes at the cost of limitations. Keep in mind that Mario Kart DS isn't an indication of the direction that Nintendo's taking with the Nintendo Wi-Fi Connection. As the company works on additional online games, the teams will most likely add features and functionality to the DS side of the link.