Seconding Rimworld, but even without mods it is an amazing game with easily 1k+ hours of gametime. My favorite mods are QoL mods, or ones that add additional flavor to my colonists. If I could only pick a single mod to install, ever, it would be Common Sense.

Outside of Bethesda and Minecraft, the other one that comes to mind is The Sims. More of a niche following, but for those that love deleting pool ladders, mods are necessary for happiness, flavor, and adding actual challenge.

There's a ton!

Project Zomboid mods are fantastic. There are insane amounts of them, and they add so much to the game.

Games like Skyrim and Fallout 4 become essentially infinitely replayable with mods. There's a tool called Wabbajack that essentially makes "modpacks" a thing for these games (and several others), and it's amazing. You can install and configure hundreds of mods in like 30 mins.

One of my personal favorite mods was "Hyrule Conquest" for 0 A.D., which is a complete overhaul of the game that turns it into a deep, lore-friendly Zelda RTS. It's still being worked on and it's still super high quality. The dev made some major changes to the play style that a lot of people love, but I personally strongly preferred the old style. It was more like Age of Empires before, but now it's more like Battle for Middle Earth and I don't care for it. If that's a selling point for you, it's very much still a great mod with a lot of love and passion put into it.

All of them. I personally find Oblivion totally unplayable unless its been heavily, heavily modded, other games in the TES aren't as bad. I suspect that's why those games still have active communities is because of modding.

Skyrim VR. The game without mods is probably one of the worst VR games ever, but with mods it becomes one of the most fun VR games.

Project Zomboid. Lots of mods that add new stuff (cars, weapons) and quality of life improvements like "Has Been Read".

I would say the binding of Isaac. The game is amazing but I now really struggle to pay without some quality of life mods

Arma 3. You could basically call the base game a platform for modding. DayZ as well as PUBG battlegrounds were originally mods for Arma.

@SevenSwell EU4's modding scene vastly improves the game, with a variety of total overhauls available. Same goes for most Paradox games actually - the modding scene is usually well taken care of.

But I'd be lying to myself if I said anything other then Skyrim AE.

I'd say it is definitly not any TES game. While the engine and released tools give amazing modding capabilities, it is still fine without mods. Back in the day, I spend 800 euro on a videocard just to graphically mod Skyrim. And I have no regrets. But I just as well regularily play on the Switch curreny, as I van continue on the train. Similarily I still booted Oblivion on my PS3 a while back. I feel TES games improve with mods, but aren't tge worst without.

Now for a game that "nééds mods" rather "thas great modding capabilities" I would say the first that comes to mind for me is Mugen. That old fighting game game with 1 stage and 1 character out of the box, but thousands of community made characters, stages, and new character select screens. It caused some videos of the ridiculous (in the best way) fights in a time YT was mainly weird but fun.

FTL has complete overhaul mods and expansions that can make it seem new even now.

@SevenSwell

Beat Saber. It wasn't saved by mods, but almost any serious player will have a number of them installed to dramatically improve the experience. #beatSaber

ARK: Survival Evolved. There are no corner pieces for sloped roofs without mods... I like a good sloped roof, and a building that's not just a square/a-frame.