Tons. There's an entire roguelike genre built around this; some of my favorites are Vagante and Streets of Rogue. There are games with procedurally generated worlds like Terraria, RimWorld, Dwarf Fortress, and Factorio. There are RPGs like Baldur's Gate 3 that have so many ways to spec your characters and so many permutations of how events could unfold based on what you did that you're unlikely to see them all.

Minecraft?

Hard to do better than the OG endless sandbox.

FTL. It’s a simple fun cheap game. Steam says I’ve played this for over 3,000 hours!

https://subsetgames.com/ftl.html#_

RimWorld. shit can go crazy with the mods a available or just vanilla.

Obligatory Rimworld shout out.

I've dumped note hours into this game than the rest of my game library combined.

I almost exclusively play single player games and honestly Elden Ring has been a huge time sink. There’s just something about mastering it that is satisfying. It has online features but they’re not required.

Minecraft, Hades, Solitaire, Civ, Gunfire Reborn, Vampire Survivor, Vampire Hunters, and Placid Plastic Duck Simulator,

Doom and all the other doom clones? Prodeus, dusk, forgive me father, there's a lot

One I haven't seen mentioned (at a glance at least) is Noita.

Getting the "false ending" is achievable with some effort, but I dare you to actually finish the game. And as far as replayability, you'll be hard pressed to have two runs that go the same. The amount of Butterfly Effect in this game from all the combinations and systems is straight up insane.

I really can't recommend it enough.

For me, it's Grim Dawn, honestly. (And Diablo before that) 10 classes to choose 2 from means a lot of new skills and builds. Tons of random loot, but also recipes to make and collect.

I mostly play with mods now. Grim Internals, full rainbow, some rep and exp gain ones, and the Item Assistant. I play solo, and have enjoyed every hour of it!

Rainworld, Cult of the Lamb, Slay the Spire, Inscryption

Xcom, xcom2

Some single player games I've replayed often that aren't roguelikes would be...

Dishonored Star Wars Knights of the Old Republic 1 and 2 Prey 2017 Hitman, but specifically the World of Assassination games Bethesda RPGs Grand Theft Auto/Rockstar, specifically for me 5 or Red Dead Redemption Dark Souls (I replay it on offline mode predominantly anyway) Dying Light Middle Earth Shadow of Mordor/War Halo MCC campaigns Mount & Blade series Katana ZERO Vanquish/other platinum games

I've played a lot of RimWorld, and I don't feel anywhere near done

My top ones I constantly replay are Factorio, rimworld and modded Minecraft java version, mainly because there's a incredible amount of mods For all of them, make themed runs for each one. Sometimes action adventure sometimes just pure automation.

Nearly 8k in Factorio and probably Minecraft, not as much in rimworld but only because I bought it about a year ago

Hades

4x games tend to be functionally infinitely repayable, since a single game often takes an eternity and there are usually many factions to play.

I particularly like sword of the stars 1 & 2. Honestly don't remember which I preferred but I know I got an insane amount of time sunk into both of them.

Risk of Rain 2 and Robo Quest are probably up your ally because you like Ultra kill

But if you want to diversify genre, here are some that I would recommend

• Card Games - Slay the Spire (Its like a card game and rogue like combined)
• Rogue Like - Hades is currently one of the top tiers in rogue like dungeon crawler
• RPG - Baldurs Gate 3, even if you end up finishing the game, how you ended up finishing it is what makes it so replayable. Each character has their own stories for you to uncover. Larian's other gem is Divinity Original Sin 2 too
• Sandbox Games - Minecraft of Terraria
• Arcade - Most arcade games are highly replayable because thats their whole selling point. Currently I am back to playing Temptest 4000
• Hack n Slash - Grimdawn, nuff said

What you are describing is essentially the roguelike/lite genre, lol. Search up some of that, see if anything looks fun.

Fallout: New Vegas, Caves of Qud, Project Zomboid, Minecraft, Terraria, Morrowind, Skyrim, Dwarf Fortress, Kenshi, Rimworld, Elden Ring, and so much more.

If you don't mind top down colony managers, rimworld is an absolute gem. The base game itself is infinitely replayable because every game is basically a story. Think dwarf fortress with graphics (well, df has graphics now but). Also incredibly easy to mod to customize or completely change your game experience.

How about a randomizer? Pick a game you like and see if there's a randomizer for it:

https://video-game-randomizers.github.io/rando-list/

I think factorio is one, even when you launch your rocket (I have more than 100 hours and I don't think....) you still can restart in a new generated world and try do to it again in a better way.

I am currently in my like 90th run of Subnautica. I'm doing an "All Cuddlefish, no native food, save the Sunbeam" run.

Rimworld would be my top suggestion, as others have noted.

I picked up Old World (excellent native Linux support BTW) during this summer sale and have not been able to put it down. If you're a fan of Civilization style strategy games I'd highly recommend checking it out. I haven't really enjoyed a Civ game since Civ 4, and Old World feels very similar but fresher and with less jank. it's got a Crusader Kings style dynasty system with randomized events that adds a layer of role playing your leader and securing their dynasty through heirs you can train/influence.

As for the repeatability, Old World has tons. Each culture plays significantly differently, and each leader has different bonuses that encourage an interesting style of play. Games don't play the same because of the mentioned event system, but also because learning new technologies is "randomized" as well. New techs are researched based off a selection of 4 drawn tech cards once you finish a previous technology. The card system makes it so you can't just rush straight to archers and dominate the early game to snowball into a power house every game, but its not truly random so you can "game" the system in your favor to get the techs you want with the tools the game gives you through either unique leader powers, or specific governor roles for example.

The game is super deep while not being off puttingly complex.

Have to throw CK3 out as my personal favorite grand strategy game (though EU4 and the like are other options). There's nigh infinite content in weaving the story of your family and realm, and mods add a whole new layer to it.

Basically any game that doesn't in itself follow a story, so you are the story (or make it). For me personally it's building and factory games, like Factorio, cities skylines (1 or 2), satisfactory, Kerbal Space program (1 only), Rim world.

This list is essentially endless.

Rimworld, Terraria, Minecraft, Satisfactory, basically sandbox games, where each playthrough is different.

Cataclysm Dark Days Ahead

https://cataclysmdda.org/

Zombie survival roguelike. It's free, open source, and a mature project.

For me, Noita. I don't recommend it unconditionally, but for me that game will forever be the only permanent game in my library. I expect it's possible that I could finish Elden Ring. I know I will never finish Noita.

Doom. No the originals. Doom, Doom 2, and Doom Final. I always go back every few years.

For me Rollercoaster Tycoon 1&2. But you could probably throw most Sim Games into here like SimCity 2k 3k or 4.

Civilization.

For the most enduring single player experiences, you really should give some grand strategy games a try, like older Total War entries, Crusader Kings, Civilization, Swords of the Stars, etc. Stuff like Factorio or Cities Skylines can also become addictive, but none of these games is action oriented.

Also, Age of Empires 2. I haven't played 4 yet, but I think it speaks volumes that, at least on steam, AoE2 has more players at any given time than 3+4 combined.

Ziggurat might be an interesting pick, as it's a roguelike FPS with magic weapons, though it might feel super neutered compared to Ultrakill. Risk of Rain 2 is 3rd person and roguelike, so every run you start from scratch and enemies will keep spawning at certain intervals, but it's a fine shooter

Fallout 4 might have a rather clunky shooting, but if you get into it, you can spend many, many hours blasting a variety of enemies, finding all sorts of places and weapons. Skyrim is a close second, while better played in 1st person, it's medieval sword and sorcery.

Deus Ex

Europa Universalis 4. And EU5 is on the horizon.

Definitely not like the games you've mentioned though.

I've been recently playing the "so called" sequel to ftl, ftl multiverse. I have gotten the standard and old secret endings, but there are hints of a third even harder to find ending.

I don't know how much is truly infinitely replayable outside of tetris, but for what it's worth I have 250 hours into dead cells and I still haven't beaten 5 cells or even reached the final biome. You'll definitely get replay value out of it, the game is fantastic.