Final Fantasy 1 - It wasn’t the first RPG, but it pretty much defined the series. It still has tons of playability, I revisit it more or less every 5 years. I still have yet to beat Warmech, and only have encountered him a handful of times.
But most of all, it’s the game that saved Squaresoft. If it had failed, we would have missed out on so many great games, including ones also mentioned in this post.
Runners up have to be Donkey Kong, which brought us Mario, which in turn restored vitality into the at home console game industry, and Double Dragon, which brought us PVP and Co-op combat.
Honorable mention would have to be that Simpsons arcade game where Marge can fight with the vacuum cleaner and TMNT 2 - Two classic, very difficult, drain your change jar games. I’d throw Mega man 2 into that mix as well.
Conflicted. I’ll give you my top 4 considerations.