When you first start out in Mario 64 DS, you'll notice one very important difference when beginning: You're playing as Yoshi. This is certainly different. You will be able to play as Mario shortly, but, for now you're a green dinosaur with a long tongue. This is the first thing that's drastically different about Mario 64 DS, you're not just playing as Mario. In fact, there are 5 different people to play as: Mario, Luigi, Yoshi, Wario, and a 5th hidden secret person to play as (who you won't find out about until later in the game). Each of these characters has their own strengths and weaknesses, different abilities, and all of them come into play in different ways. Mario, as usual, is your general good all-around person. Yoshi has his tongue, and his float jump. Wario has his strength. All of these different abilities come into play many times throughout the game. While you only can be one person at a time (there's a room in the castle you go to where you can switch who you're playing as), in some levels there are blocks with hats which will let you temporarily change to one of the other characters.
The next thing that's different is, there's not just different characters to play as, but different goals to accomplish as well. The original Mario 64 had 120 stars with goals to accomplish. Mario 64 DS has those, but many more in addition. While I won't give a specific number so as to not give away too much about the game, there are many more than the original 120. As well, even with the original 120, with the new characters there are now new ways you can go about accomplishing the goals. So, if the new characters weren't enough to make you feel like you were playing a new game, the new goals make it even more apparent. As well as these new goals, another thing is that there are rabbits scattered around in various places. Catching these rabbits with the different characters leads to the next dramatic different. Minigames. Oh minigames. Are there ever minigames. While I don't want to minimize the importance of the main game any, this game is worth buying for the minigames alone. While you only start out with a couple, more minigames are easy enough to pick up. These minigames cover a huge variety of topics, from card games, to tests of skill, timing, reflexes, and many other things. The touchscreen comes into play many times in these, as you will be pulling back slingshots, poking at the screen to keep someone afloat, drawing lines to make paths or create platforms, and many more things. The game keeps high scores for all the different minigames, so, it's easy to just get lost in one of them trying to improve on a score. These games are an absolute blast to play, and, as I said, are worth the price of admission by themselves.
On the topic of the touchscreen, comes the one downside to this game. Mario 64 was, in many people's opinion, the absolute pinnacle of game control and camera control in a video game. In many people's opinion, it's a standard which still hasn't been improved upon. Much of Mario 64's control came from the fact that the N64 controller was basically designed around this one game, with the analog stick and C buttons and everything. Well, that's where the DS is lacking, it doesn't have an analog stick, only a D pad. Mario 64 DS implements a few different control options to attempt to work around this shortcoming. One is, obviously, to just use the D-pad for movement, which works alright, but feels awkward trying to move around in a 3D world with only the directional pad. The other, better option is, the touchscreen can be used as a sort of "analog screen." That is, when you place your thumb (or stylus, but that's not really recommended) on the screen, where your thumb is, is the "center" of the analog "stick." When you move your thumb up, it's the same as pushing a stick up. Obviously you can move your thumb in any direction on the screen you desire, and it's the same as pushing the stick in that direction. The system also comes with a thumb strap that you can put around your thumb, which has a little plastic piece on the tip which allows your thumb to slide around the screen easier. This really is the best setup. In the normal setting you use your left thumb for the screen and your right hand for the buttons. There is, however, a hand reversing option where the 4 directions on the D pad are assigned the functions of the 4 face buttons, so if you'd prefer to use your right hand instead of your left for the screen, you can work it this way as well. It works pretty well, and if you'd never played the original Mario 64 you might not really even give it a second thought, it's better than quite a number of games out there. However, the fact remains, it's not Mario 64's controls, and as such, it feels awkward. There is, unfortunately, no getting around that. It's good, but it's not Mario 64.
As far as graphics and sound. When Mario 64 came out, it was one of (if not the) most expansive games ever, with huge, varied landscapes. Dry deserts, dark caves, beautiful oceans. Well, the graphics for Mario 64 DS have actually been improved. Textures have been smoothed, colors have been improved, a general facelifting. The beauty and variety of Mario 64, made better. The sound has been excellently transferred over as well, with the DS's stereo speakers emitting it perfectly. As well, there are many new sound effects added to the game, each of the different characters have their own voices and sounds and reactions and everything. Both graphics and sound are everything one would hope for and more. As far as the touchscreen, in addition to movement it's also used to give a map of the course you're in, which, while not spectacular, is a welcome addition.
Even if you've memorized every single thing from Mario 64, it's still going to take you a decent amount of time to go through everything. There are enough things which have been moved around or changed where you're not going to just be able to breeze your way through, even if you don't try out any of the new things. While you don't have to collect every single star and coin in order to beat the game, they're there as challenges to go back to. Even once you've beat the game, maybe you played as Mario most of the time through, you can get an entirely new feeling just playing through again with Yoshi, reaching areas you couldn't before, taking different paths, and just a new overall experience. Beyond that, even once you've played the main game through over and over, there are still the minigames to come back to. Whether you play them by yourself or challenge a friend to beat your score, they provide challenge. As well, many of them are just fun to fool around with and play. Drawing trampolines for Mario to bounce off can be fun even if you don't particularly care about the points.
Simply put, if you loved Mario 64, you will love Mario 64 DS. The core game that you loved the first time is there, and you can now play it on the go (which if you are out often is a key enough point on its own). As well, so many things have been added, moved around or changed where there are many new things to try out and explore even if you've beaten the original game countless times. The new characters add many new experiences to the game. Plus, again, the minigames are full of nearly endless fun, and will keep you coming back even when you don't feel like playing through the main game. The control works well enough, but, unfortunately, it's just not the same, and this is the only thing keeping the game from being a perfect 10. Even with that, however, if you loved Mario 64, you will love this game. If you own a DS, there is absolutely no reason in the world not to own this game, it's absolutely spectacular. Even if you don't own a DS yet, this game is reason enough by itself to buy the system. The core gameplay of Mario 64, with countless new additions, and minigames. A must-buy.