1990 - Super Mario World
The early 90s were a mess of cross-regional release dates and associations between year and video game. Super Mario Bros 3 dropped in the US in 1990 - the same year Japan was tucking into sequel Super Mario World on the eye-widening Super Nintendo. While that console then dropped in the US in 1991, the UK had just gotten 1988's Mario Bros 3, and it wouldn't be until April 1992 that we'd get a SNES for ourselves.
Cut through all that and apply the rule of "when did the definitive version of a game first appear" though, and Super Mario World rightfully dominated 1990, remaining feature-complete from then on out.
An essential 2D platformer that hasn't aged a day, Super Mario World's music, feel and set of levels is immortally enjoyable.