There is little I can say that hasn't already been said about this game. There is only one thing I can say: buy this game. Don't have a 64? Get one. Better yet, get a Game Cube and get either Master Quest or Collector's Edition for it; I suggest the latter because you can get Majora's Mask AND the first Zelda games with it.
In any case, OoT takes place before all other Zelda games and serves as a back story to the villian Ganondorf. In other games he appears as the pig monster wizard Ganon, but in this one we see what he was before the change.
However, the back story of Ganondorf is not the draw of this game. It's the game itself. Beautiful graphics, countless hours of gameplay replayability, fantastic music and wonderful control. This truly is the best game for the 64 and the best game of the Zelda series. Fact.
This game is REQUIRED to live the rest of your days. Punch your piggy bank in the nose and grab all the coins and demand more from the shreds that was Rich Uncle Piggy. You need this game. Now.