ExploderWizard
Hero
For me, it will be remembered as the first WOTC edition of the game that made me excited to run a campaign.
A level one wizard killing a tarrasque while riding a horse using nothing but a cantrip.
& 1e players. I stopped playing while my group was transitioning to 2e & the Forgotten Realms (almost 30 years for me).
Simplicity and easy to learn game system. My family and a hand-full of friends all picked it up fairly quickly and none have ever played any table top RPG before. My daughter even had a D&D sleep-over birthday party and taught her friends to play (& they all loved it)
Simplicity; individuality (DM rulings = home brew elements baked in); rejuvenating lapsed players back to the game; Advantage/Disadvantage (see Simplicity).
But it all depends on timescale... "what's a 'tabletop' daddy?" "Quiet, son, or the cockroaches will hear us" "but daddy, what's a game?" "too late! They've heard us. Come on, kneel, say the anthem, "two legs bad, six legs good"".