Cassette Beasts, it's like Pokémon far more different than other pokeclones, and far higher quality imo. The beast designs are great, and there's a cool fuse mechanic you can use to fuse any two Beasts, with unique art (over 16,000 possible fusions). Also the shiny-equivalent is better done and actually useful.

The Binding of Isaac. One of the GOATs for me.

Looking at my steam:

Total: Factorio. Though I do think I need to put that one on hold after I'm finally done with my current save - which is not far out anymore. Also, this game has multiplayer so it may technically not count.

Recent: Derail Valley, a very down-to-basics train simulator, focusing on cargo rail in a fictional rendition of an area in the Balkans. They recently put out a major update, which makes all kinds of simulation features much more expansive.

Outer Wilds. You can really only play it once though but it’s amazing!

BPM: Bullets Per Minite

Doom meets dungeon crawler meets Crypt of the Necrodancer.

The Binding of Isaac. It is too addictive

Tony Hawk's Pro Skater games 1 through 4.

A bit more than once a decade I play them on emulator and try to 100% them. Great fun. I also try to make sure to visit the locations in the real world if I'm on holiday nearby where they based a level.

It's kind of sad that the Venice Beach area hasn't existed since the 90s.

Edit: I did just realise this thread is about PC games, but I do play them on PC albeit through a PlayStation emulator. I do believe the games are available on PC.

I love the Fallout universe and crafting in games, so with the amazing mod community I've wasted (?) nearly 6,000 hours on Fallout 4.

I know it's arguably the weakest of Fallout 1-4 and New Vegas, but it became a refuge for me to escape from the real world into.

Good ol' Skyrim. The possibilities to break the game are nigh endless.

Workers and resources. It's like cities skylines on steroids.

Subnautica and Planet Crafter.

The best "just one more thing!" games I've ever found. Huge chunks of time just disappear for me and the people that I've had play it. Very rewarding.

Civilization 6, this game is a time sink

Cyberpunk 2077 story

My friends make fun of me for it but...

Football Manager.

I know it's a spreadsheet simiulator but I can't stop.

DemonDarkBloodEldenSoulsBorneRing.

Edit: Of those that are on PC, anyway. I got tired of waiting for even an announcement that a BB or Demon Souls port was on its way and got a PS5 just for those two things back in January.

Dying Light, absolutely fantastic pakour zombie smasher with one of the best cities in gaming. Bought it originally (on a disc) many years ago and played it so much the disc died and I was inconsolable until Epic gave away the ultimate edition and I was finally able to play The Following DLC.

Now I go and look at Dying Light 2 on Steam and wish my stupid country wasn't so damn expensive, even on sale at 50% off it still costs almost as much as a brand new AAA game in the states. Regional pricing my ass, we always get stung so hard for tech down here.

Since nobody has mentioned it, I'll throw in "X4: Foundations". The X series is janky in places but oh so satisfying if you can get past the jank. Build a military empire to take over the galaxy, or maybe a trading empire. Or maybe you want to become an industrialist and build huge stations to print money. You can be a pirate or a salvager or any combination of the above. And there are tons of interesting mods if you get sick of the vanilla game.

Love this game!

My go to would be Skyrim, but i actually stopped playing about a year ago. My current one would be cyberpunk but i'm waiting for the dlc and playing diablo 4 atm.

Vampire Survivors I just love that game, after that Tetris.

Transport Fever 2. It's like Transport Tycoon (/Deluxe) from the 90s/OpenTTD but way more beautiful and 3D.

Fallout 4 ☢️

Ultima and Wing Commander, I know I'm showing my age but I guess it's the nostalgia. I still go back and play through them.

Neverwinter Nights, I enjoy playing some of the campaigns and modules every so often, trying out different builds.

Warcraft 3, just for the original campaigns and also the stupid amount of custom campaigns made by the community.

Deep Rock

Rogue Legacy 2

If you enjoy platformers and roguelikes, you'll like this.

Rollercoaster Tycoon / OpenRCT2

Transport Tycoon Deluxe / OpenTTD

While they do now have multiplayer modes thanks to their corresponding open source projects, I still think the spirit of these games is firmly in the single player pc game category. Best of all they're both free and available on any OS!

Titanfall 2's campaign. I don't replay a lot of games, but I've played through that one a good few times.

Solitaire

Outer Wilds, played it once loved it so much I still get tons of enjoyment by watching others do full play throughs

Definitely Civilization in general. There’s a lot of other games I like that are completely different, but year after year I come back to the Civilization series. And even though they peaked at Civ5, it’s still one of the few games I’ll preorder as soon as the next one is available.

Stellaris and Factorio

Minecraft

doom

Minecraft Rimworld Cities Skylines Satisfactory

Factorio, Rimworld, Terraria. In no particular order, they're all perfect at what they do.

Medal Of Honor 2010 & Call Of Duty 2