I say Super Smash Melee. no other game has perfected the party-fighting genre like that one. the huge number of changeable fighting options, items, game modes, characters. it's just like a perfect game
it says a lot that tons of conventions and places still host large tournaments for the games and that generally people replay it with friends very commonly.
I understand those saying Mario Galaxy though, mega creative mindset in terms of platforming and Mario in that game







