All the classic Mario characters are here: Peach, Yoshi, Donkey Kong, Koopas, Bowser, Luigi, and many more, as well as Mario himself. This is the first shortcoming in Double Dash. What is this shortcoming? You have everything from the start. All characters, and thats it. There are a few Karts to unlock, but they hardly differ from the others and often end up being rehashes with a different color scheme. It really cuts down on replay. This stays true with the tracks. There are four circuits with four tracks each. The final is unlockable. While each of these tracks are fun and unique in their own right, there isn't a whole lot to see and do, especially after you unlock the final circuit. Besides the main circuits to race, there is also a battle mode, which is fun for maybe an hour or two, and a time trial mode, which proves to have the most replayability, more so for those who are high score maniacs.
Racing itself has always been Mario Kart's strong suit, and it proves no different in Double Dash. Scattered along the tracks are items, which can be thrown at you oppenents that have different effects: one shrinks ememies, thus slowing them down, one chucks a Koopa shell that tracks the opponent, and so on. In Double Dash, you ride with another player. The player in the back seat throws the items while the other drives, allowing for two player co-op. Its certainly a nice addition to the otherwise unchanged gameplay.
So in the end, Mario Kart has undeniable quality to it, but the package has little to offer. Mario or casual racing fans shouldn't miss it, but the rest should pass it up as a rental.