i think people use the terms must-watch and must-play too easily. like, i don't think the world has lost something deep because i didn't see episode 37 of seinfield.
or saying something is a must-play because it's culturally significant, like, why must i play the original worms? i guess if i loved the series.
a really great and culturally significant game, one of the first rpgs, if you're into those, is ADOM, Ancient Domains of Mystery. it's a massively detailed and incredibly fun little game from the early 90s. It's all text-based, but it even holds up today. main complaint is that the control scheme is really bad, compared to modern games. instead of optimizing with a few buttons like we do now, they have the old habit of keeping a button for literally every possible action. so dont accidentally hit 7 on the numpad or you might convert to judaism.
also, it's the game that Corruption of Champions, the game nobody will admit they've played, is parodying. the random player mutations are ripped straight from adom.