It used to be that Chrono Trigger was my go-to answer for this, because that is to me the gold standard of RPG games. Its not about being the first, longest or most sold, but rather the most complete. And CT is easily the very best exprience from every metric i can think of.

I say "used to be" cause I dont really think this question has a 100% satisfying answer, i dont think modern audiences care. Theres other games that might feel more relevant from a "historical" perspective, but current gamers would just react Meh to them.

Any Mario side scroller, that's the most quintessential game series to ever quintessense.
If I have to pick one, Super Mario World.

1v1 Naked Twister

Clair Obscur : Expedition 33.

Never played it, but out of the 3D Zelda's I've played the only one I really like is Breath of the Wild.  I'm skeptical that I'd like OOT.

As for the topic:
If "everyone" includes non-gamers, then I'd say Tetris and Ms. Pac-Man.

OneShot, specifically the original version from 2016. The updated one from 2024 has some cool additions but it loses something that makes the original a unique experience that you can't get with any other art form. It's truly something special due to how it uses the medium for storytelling and character development.

I'll also recommend Doki Doki Literature Club for the same reason. Funnily enough it also has an updated version that loses an aspect that makes it such a unique and special experience so while that version is good for a replay the first time should for sure be with the original.

In general video games that use the medium to their advantage to do things other mediums like film cannot do are some of the coolest games out there.

I won't say old games because due to outdated graphics it won't have much impact.
I would say Demon's Souls, Resident Evil 7 or Claire Obscure.

"game you believe every one *needs* to experience?"

1. Needs timeless visuals.
2. Needs to be simple for all ages.
3. Needs to be easy to access.

Tetris and Super Marios World (SNES)

Undertale.