Gaming

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'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.

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.

Europa Universalis 4. And EU5 is on the horizon.

Definitely not like the games you've mentioned though.

The binding of Isaac.

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

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.

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.

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

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.

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.

Dungeon keeper.

Any of impression games latter worldbuilders (pharaoh, zeus, emperor)

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

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.

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.

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.

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.

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.

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

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

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.

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

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

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!

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.

Spelunkyyyyyyy!!!

Doom? Does it have any wads you can play on... like myhouse.wad...

I can play Control over and over again.