Having never played to N64 version, this was entirely new to me. My first DS game, and one of the best!
The graphics are superb, the story is intriguing, and the game-play is fun, but it lacks good use of the touch screen. Unless you really want to challenge yourself, you'll probably only use the D-Pad to move around, but the stylus is an option, albeit a more difficult one. If you grow tired of the game itself, the mini-games are a fun way to kill time, and some are actually very good.
In closing, SM64DS is great simply because you can put it away from a few weeks and come back to it easily. Unless you remember everything from the N64 version or you are one who likes to finish entire games in one sitting, this will probably take a while to complete. Great control, great graphics, great bang for your buck.
Go get it.