Without a doubt the greatest Zelda game to date, possibly the best game ever. The story is fantastic, the gameplay is absolutely superb, the graphics are wonderful, and there is just so much to do in the game outside of the story that you'll play for ages.
By far for me the best aspect of this game is the control system. I have yet to see an action based console game with anything nearly as easy to control as Ocarina of Time.
There's also so much variety in the dungeons and the main storyline that I never got tired of going through the game. There was almost always something new and unique in each dungeon.
This is one of those games that you really need to go out and get an N64 to play even if there's nothing else for the system of interest. It's that good :).