I bought the nintendo 3ds just for this game and i was glad i did. The whole game is completly in 3d although i didnt play the game in 3d all the way through as i felt it hurt my eyes after a while although at times i thought stuff it as the scenery/cut scenes were so good! even in the normal 2d mode the game is a lot sharper - making the graphics fantastic.
Zelda OoT is also a huge game - i feel with certain nintendo ds games the games are small, making them quick and easy to complete, however with this game there are probably about 12 dungeons and a million different side quests to complete.
The game is excalty the same as the N64 but after you complete the game, you unlock a master quest (a harder version with certain things back to front).
All in All, a fantastic game, definelty worth the money. Shame the game hurt my eyes after a while but even the 2d version is immense.... A must have!!!! Buy NOW!!!