Subnautica

Tunic

The Legend of Grimrock 1 and 2 (I’ve convinced 0 people to try these)

Stardew Valley

A ton of great suggestions here already. Let me add some more.

Dead Cells: amazing 2D action rogue lite with metroid Vania elements. A game that keeps getting updates faster than I can play them. And they are good.

Battle Brothers: hex based tactics and management game where you play a band of mercenaries in a fantasy world. It’s insanely deep and we’ll made.

There are a lot I’d recommend, but I think the only must-play for me is Cave Story.

When I was growing up, Cave Story was like the paragon of games as art, and was a major inspiration behind me making games as a hobby and getting into software development professionally. Cave Story was made by a single talented auteur, not for profit, and released for free. And it was as good as Metroid and Mario, or maybe even better. It proved to everyone that such a thing was even possible.

I think the only indie game that could possibly compete with Cave Story for the title of “most influential” would be Minecraft. Though Minecraft should probably be disqualified from that title for having sold out to Microsoft as soon as it started to get big…

I would say Hades.
The gameplay loop, the art direction and the story are all very good.

Disco Elysium blew me away with the writing, absolutely a must-play.

I usually play indie stuff. It feels more like a labor of love than big, corporate AAA titles. That said, the only two must haves, Imo, are Omori and Dwarf Fortress. Neither game is perfect, but they are both incredible, unique experiences. With Dwarf Fortress, enter with plenty of prior knowledge, but with Omori, play it blind. Very important for both games.

Oh disco elysium for sure. Fantastic crpg.

Factorio has been my crack-torio for many years. Satisfactory may have better graphics, but I prefer the simplicity and depth of Factorio.

Subnautica. One of the best experiences I’ve had in gaming.

Outer Wilds. One of the most creative and thought-provoking games I’ve played. Definitely go into this one knowing as little as possible about it.

Hollow Knight also deserves a spot here, but personally I preferred Salt and Sanctuary.

Celeste is one my favorite games of all time!

Superhot, Katana Zero, Hotline Miami, Celeste

FTL, Into the Breach, Celeste, Hollow Knight, Banished

The games that stuck with me are (in no special order) Paradise Killer, Sable, Disco Elysium, Gris and of course What remains of Edith Finch.

I usually only play the large bombast blockbuster titles, but Actual Sunshine did leave me speechless.