Tacoma: I saw this mentioned but it's absolutely worth a shot. The gameplay is distinctly well built and the story is superb. Tacoma is best experienced with one person playing the game and a few others trying to figure out what's going on silently, or collaboratively.
Gone Home: From the same people that did Tacoma, a story that explores what happens when you have to unravel a few family secrets you didn't realize you had to conquer.
Oxenfree: Something is wrong, and the story doesn't let on what exactly. I had to play this
2067: Read Only Memories. Point and click adventure game that covers some extremely mature topics in an approachable way. Racism, classism, the pressure of being a minority, all these come up. You're a writer turned unwitting detective when a rogue AI breaks into your house and begs you to help find the killer.
Opus Magnum, and any of the other Zaktronics games: They're absolutely nerdsniping, with deep techincal lore that makes you think long and hard about an answer. Opus Magnum is absolutely a game that you will spend some time trying to optimize down to a tee.
Orwell: You, civilian, have been tasked with assisting the training of an online learning AI to help categorize and assist in law enforcement. How much free will you have in that process... well, that's not for you to decide. (n.b. I had to set this one down for a while; There came a time where I felt like I was fighting the central conceit of the game before I let it go)
Snakeybus: you are bus. you collect passengers. More deliveries of passengers = longer bus. You see where this is going. The physics engine is... part of the charm.
Snapshot: What if cameras could transpose a whole world? Side scrolling platformer, but where you can snag a snapshot of the world to grab items out later.
Slipstream: A classic OutRun Arcade title, thrown in since it's cheap and a great mind-melter. Unlike OutRun, however, it doesn't make things unfair... Any failures are your fault, not because the game wanted to screw you over.
Later Alligator: A slightly paranoid alligator is worried someone's taken out a hit on him. The question: Who?
Eversion: Mario clone but with the warning that not all is right. Cute turns to creepy.
VVVVVV: vvvvvv
Night In The Woods: There's no way around recommending this game, it's just so well written. Not a lot of action but some definitely mature conversations about accepting growing up.
Verlet Swing: Vaporwave speedrunning game where you catapult yourself off things by leveraging momentum.
The Stanley Parable: This is the story of a man named Stanley. The narrator of this story is not Stanley.