Great update of a classic, just with poor controls
One of the main differences in the DS game is the controls. There is a touch screen movement option, but it really doesn't work very well at all. Therefore you are stuck with using a control pad, which is absolutely lousy for 3-D platformers. Add the fact that you have to hold Y to run and you get pretty mediocre controls.
The controls are the main things that hurt SM64DS. The rest of the additions are really great. One of the most drastic differences is also the graphics. They're really nicely done and look a whole lot better than they did on the N64. This was also a great way for Nintendo to showcase the DS' graphical capabilities early on in the system's life, and they did it with much success.
Another change is being able to play as four characters: Mario, Luigi, Wario, and Yoshi. The really weird thing about this is that you actually start the game as Yoshi (???) and you have to rescue Mario at a certain point. Playing as Yoshi is a drag, because he's really no fun to have to use. Mario is your best bet, but after you rescue Luigi and Wario you will sometimes have to go back to a special room in the castle to change between the characters to use their unique abilities to do certain missions. Luigi is pretty fun to play as and Wario is ok.
If you thought the N64 game was big, wait till you hear this: SM64DS has 150 stars, 30 of which were not in the first game! This is a huge upgrade in length and value and is a really nice thing to have.
The last thing I want to talk about is the minigames. As you play, you'll find bunnies around the castle. These bunnies carry keys that will unlock a minigame for you. The minigames are also another way Nintendo decided to showcase the system early on, as they all make fun use of the touch screen and are good for some varied entertainment in between collecting stars.
Overall, SM64DS is a worthwhile remake. Not only does it have 30 more stars, but the visuals are updated, there are minigames, and also four characters to play as. While not everyone will be happy with the changes made to their beloved N64 classic, the DS remake is still a fun game. If you haven't played the N64 game, I recommend you pick this one up. Otherwise, you may or may not want to bother with the game; it just depends on your own tastes.