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.
Another great roguelike is Hades, which may or may not have dominated my video game attention for the last 8 months.
Minecraft?
Hard to do better than the OG endless sandbox.
Definitely was my first thought. I think that I've spent way more time on that game than I'd like to admit.
FTL. It’s a simple fun cheap game. Steam says I’ve played this for over 3,000 hours!
Rimworld, Terraria, Minecraft, Satisfactory, basically sandbox games, where each playthrough is different.
Obligatory Rimworld shout out.
I've dumped more hours into this game than the rest of my game library combined.
Edit: typo
A significant number of comments have mentioned Rimworld, guess I'll install it. Thanks for your recommendations!
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.
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,
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
Balatro
Hades
RimWorld. shit can go crazy with the mods a available or just vanilla.
I dunno, I only have 3417 hours played in Rimworld, I'm not sure that qualifies as infinitely replayable. ~/s~
Don't give up! You're close to finishing the tutorial!
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.
Doom and all the other doom clones? Prodeus, dusk, forgive me father, there's a lot
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.
Minecraft, Hoplite, Shattered Pixel Dungeon. You probably want a good roguelike.
Rainworld, Cult of the Lamb, Slay the Spire, Inscryption
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.
Kenshi is infinitely replayable, imo.
From the alternate starts, to the different ways you can even play the game (wanna be a lone trader, traveling from town to town buying and selling goods? Want to be the ultimate warrior who can go toe-to-toe with the Spider King? Wanna build a city/outpost where you can be totally sufficient and build up your own personal army to take over the world?), to the sheer size of the world. Plus all the awesome mods that can add so much to the game that already has a lot. You start off with your skills at 0 or in the low tens, and you will get your ass handed to you on an iron platter until you actually train up a bit; but even a high or max level character can still get fucked up by the wrong group of enemies.
I have mods that add a couple new factions (the fungoids are OP), flesh other factions out a bit more with more weapons and gear, and other building mods and some QoL mods so I can truly tailor my experience how I like it.
It plays kinda like an RTS with a mix of RPG elements.
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 and risk of rain 2
Slay the Spire
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
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.
The binding of isaac: rebirth and dlcs
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
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.
I am currently in my like 90th run of Subnautica. I'm doing an "All Cuddlefish, no native food, save the Sunbeam" run.
Anything with procedurally generated levels, like roguelikes/roguelites. I can personally vouch for the longevity of Slay the Spire, for one specific example.
What you are describing is essentially the roguelike/lite genre, lol. Search up some of that, see if anything looks fun.
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!
Minecraft, especially with mods.
Roguelites in general. My favorite is FTL. Also has good mods.
Kerbal Space Program, for sure. Skyrim is another.
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.
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.
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