A Repackaged, Improved Mario Platforming Classic
This game is a lot of fun. You start playing as Yoshi, and must rescue other characters throughout the game (including Mario) who then become playable. The levels are very well-rendered, and feature the fun characters that have made Nintendo famous (Princess Peach, Toad, etc.)
As well as a slightly revamped Mario 64, the game also includes several unlockabl mini-games that are a lot of fun. Making ample use of the touch screen, these games are quick and fun time wasters that I've actually spent as much time playing as Mario64 DS itself!
All in all, unless you really hated Mario 64 or dislike platformers, this is a good game. For any fans of Nintendo's Mario games, this is a must own.