Bridge Base online. The best replay value in the world.
If you want me to answer one of the new games (Bridge is hundreds of years old), I'll have to go with OoT.
Melee is very very close, and SMG is also right up there, and of course, a gem many missed - International SuperStar Soccer 98 - a game that beats every football game ever created, and it's form 1998! So it is hard to say, but I'll go with OoT, as it is actually the favourite game of everyone in my family but my dad (his is ISsS 98)
FE:RD was also awesome, and I think that if a game should ever dethrone OoT, it would have to be either a SRPG or Brawl.