Do you know any singleplayer games that are infinitely replayable?

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.

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

Hades

Classic Doom 1 and 2. There's gotta be over 100 levels if you count TNT and Plutonia, which I think were sold as Final Doom? Anyway, if you just get the base games for 1 and 2, there are thousands upon thousands of community made maps, including some total conversions, so you can play new Doom content until it physically pains you to continue.

Of course, I feel obligated to mention that even though it would be super easy to pirate the WAD files and play with a free modern source port like GZDoom, like absolutely trivial to find copies of DOOM.WAD and DOOM2.WAD floating around the net, probably showing up easily on Archive.org, but... Um... Where was I going with this? Oh, right, don't pirate. Cheap on GOG last I knew.

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

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

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!

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.

The binding of isaac: rebirth and dlcs

Honesty I'm shocked nobody has mentioned Tales of Maj'Eyal or ToME for short. Extremely deep roguelike with story and it is getting expansions ans updates all the time.

Also it is open-source, so can be downloaded for free, but I would recommend you also buy it in steam for instance to support it.

Slay the Spire

Risk of rain and risk of rain 2

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

Closest I can think of to infinitely replayable games are rougelike games like Slay the Spire, Peglin, Shotgun King: The Final Checkmate, Backpack Hero, etcetera, and sandbox games like minecraft (or Minetest if you don't feel like spending money and/or don't already have a minecraft account).

Though, with the rougelike games I mentioned, there are upper limits to increasing difficulty levels.

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

Anything with procedurally generated levels, like roguelikes/roguelites. I can personally vouch for the longevity of Slay the Spire, for one specific example.

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.

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

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.

Kerbal Space Program, for sure. Skyrim is another.

Look up project brutality or brutal doom. Those are great doom mods with a lot of fun gameplay. I used to play that for hours.

The Anno series is pretty cool. It's like playing crack. I've been playing 1800 recently and it feels like an instant classic.

The elder scrolls games are great for this. The further back you go the more replayability there is IMO. Morrowind is goated.

Dungeon keeper 1&2 are both a lot of fun, and have lots of custom maps. The original dungeon keeper even has a full engine rewrite which is really good.

If you want to try map painters, Crusader Kings 3, EU4, and Victoria 3 are all excellent and in depth games, with a lot of replayability stemming from all of the different ways to build up your nation in the sandbox.

Rimworld, dwarf fortress, etc. Have fun!

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.

War for the Overworld (I have many thousands of hours in this)

Settlers 2 Gold

(Both the above have a lot of user generated maps, which has given them most of their longevity.)

Factorio

Borderlands 2 has a lot of replay potential without getting boring. It never plays the same way twice. The weapon drops are very different each time through. Don’t forget the DLC. The rest of the games in the series are fun too, but BL2 seems to be where it peaked for me.

Planescape: Torment is extremely replayable. I've been playing it every few years since I got a copy in I think like the early 2000s. It may be that this has something to do with having gotten to play it a little bit in the 90s but not having gotten to play the whole thing. There was a lot of anticipation there.

But I don't think it's just that. It's incredibly responsive to choice, and it's one of the first games I can recall with things like faction reputations and alignments. There's a lot there to dig through, and even once you have, it's always cool to wander around Sigil. It feels very alive.

The other one I end up replaying over and over is Shadowrun for SNES. That's not so much infinitely repayable though as just a really great game that I'm happy to run through.

Stellaris, Rimworld, the Sims, and a lot of stragedy games.

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

The binding of Isaac

Tetris maybe (too close to candy crush)

If you into emulators the SNES has a lot of good arcade ports, those are high score based

Dyson Sphere Program is dangerously replayable to me. Hundreds and hundreds of hours sunk into it

Cataclysm Dark Days Ahead

https://cataclysmdda.org/

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

Europa Universalis 4, Crusader Kings 2 and 3, Mount and Blade Bannerlord/Warband, Star Sector, Battle brothers, Path of Exile, Last Epoch, Grim Dawn, Stellaris.

Europa Universalis 4. And EU5 is on the horizon.

Definitely not like the games you've mentioned though.

Deus Ex

Generally games with random elements are considered to be good for dumping tons of hours into. So games with randomly generated worlds like Minecraft, roguelikes, strategy games that are always variant just because of the nature of AI actions always being a little randomized, and other stuff like that. So maybe like Minecraft, Dwarf Fortress, Crusader Kings 2 or 3 as like a basic list. But really the game that's going to be the most replayable is the one you don't get tired of. I've beaten Thief: The Dark Project hundreds of times and that game is a relatively simple level-based stealth game with no random elements and not even especially huge levels.

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.

You can get hundreds of hours out of Binding of Isaac, easy

Strictly speaking about single player games, as in no rogue likes and such, Max Payne 2 is probably the game I played most times over the years.

If you're into boomer shooters, you can't go past the original doom for infinite playability. Literally 30 years worth of user created content and mods.

Many ppl suggest rougelike/lite and sandbox games I want to also add games with a good mod community and have a lot of side quest like Skyrim, they fit the replayability criteria because when it starts to feel the same can you add mods that change things up. I have done thousands of hours in Skyrim and never finished the main quest 😂 I think Balders gate 3 will also live for a long time. Many rpgs seem to get a lot of mods and games like Balders gate change a lot depending on what you do and how you play.

But you seem to want some kind of fps so warframe would be better, you can play alone or with friends. Just like ultrakill do you jump around killing, you can use, swords, guns and magic depending on your build (there are many). Doom would also fits your style of playing I think.

Otherwise management games is a time sinker. But most do not have fighting elements where you yourselves fight. Cult of the lamb tries to be all of it, it has action/fighting and management you can even decorate if you are into that. Pretty good for those who want it all. The devs still updates it too.

My most played games outside of actually multiplayer games are arpgs. Diablo(mostly 2 and 3), path of exile, last epoch. Diablo2 and last epoch can be played offline, PoE can't. And yes, they're technically online multiplayer games but most people play them alone so they might as well be single player games to me. After that my most played games are RPGs and rogue likes. Plenty of good suggestions for that already

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.

The binding of Isaac.

I've been playing it on and of since the flash game released 13 years ago.

The one I never get tired of replaying is Mafia 2. Maybe a weird choice since it's very linear and every play through is pretty much the same. But the story is just perfect for me. The gameplay perfectly suits the story, nothing especially clever, just well executed.

Then there's games like Binding of Isaac or Dead Cells where every play through is different.

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.

X4 foundations and relevant DLC. I have multiple saves with over a year worth of playtime

Super Metroid. The game really opens up if you spend a bit of time learning alternate routes and sequence breaks. Many of them are kind of easy too. Besides all that, I just feel weirdly cozy in the depths or outside in the rain. It's also a shortish randomizer if you go outside of the vanilla experience with like 100 places to check.

Honestly, Skyrim. With so many great mods available these days, you can literally turn it into a whole different game. And with modpacks on Nexus, Wabbajack or similar sites, it's easier than ever. I'm just getting back into it myself after 3 years, but I'm still a big fan of getting into the nitty gritty of it and configuring everything myself.

Diablo 1/2

Factorio and RimWorld immediately come to mind. Even with the base unmodified game, you’ll likely get several weeks of gameplay out of Factorio. Then if you dive into modding, you’ll never put it down. Multiplayer is really nice too. And their big DLC just got announced, and is planned to drop in a few months. So now would actually be a great time to dive in, because you’ll get access to the DLC about the same time that you’ve burned through the content on the base game.

Dynasty Warriors 2, Dynasty Warriors 3, Dynasty Warriors 4, Dynasty Warriors 5...

I put multiple thousand hours into Mount blade warband, Crusader Kings 2, Europa universalis 4, and more.

Football Manager 2016 was the first version I tried. I put 1,500+ hours into it and only stopped because I decided to upgrade to Football Manager 2018. I'm on 2024 now at ~400 hours.

I can play Control over and over again.