Dungeon Crawl Stone Soup: http://crawl.develz.org/
Screenshots: http://crawl.develz.org/wordpress/screenshots

It’s a traditional roguelike, so basically a puzzle game with procedural world generation and permadeath.

I’ve played hundreds, if not thousands of hours of that game. Still haven’t beaten it even once. ¯\_(ツ)_/¯

It’s extremely niche, so I doubt I can sell anybody on it, but here goes anyways:

The difficulty curve is extremely tight and it has convenience features (auto-explore and auto-combat) to skip the boring bits, so there’s almost never a moment where you mentally idle while playing.

It’s also turn-based and takes just a couple seconds to start up or close down, which is really convenient for quickly playing a few turns every now and then.

I also do like the, uh, minimalistic art style. Like, it’s downright ugly, alright. But much like a book, your brain fills in the blanks with the best graphics.

And also much like a book, it is really good at telling stories.
Like the time I fell down a shaft into an ancient grave and had to fight my way out of there.
Or when my god was gifting me nothing but garbage the whole time before casually dropping an ice-fire dual blade.
Or when I was fighting off the sirens that were dragging me out into the sea, only to find a kraken waiting there.

I especially also love that these are not some run-off-the-mill stories fabricated by a writer. There was a range of chances that all aligned to produce that particular tale. And they are my stories, I experienced them. I didn’t just read about them.