I feel like the games that are so popular it becomes a template for hundreds of other games. Games that basically made their own genre. Or games that people still talk about 20 years later because they are filled with nostalgia. Games that gave you an experience you won't ever get in any other way with other media.

Tetris, super Mario bros, pacman, metroid, zelda ocarina of time, doom, God of war, grand theft auto, the sims, halo, bloodborne.
Or final fantasy 7, 10, the mother series, journey, the last of us, undertale, shadow of the colossus.

For me right now, it's stardew valley. Simple, but just the right balance to enjoy yourself. And zelda: breath of the Wild.