Something extremely re-playable from your childhood that you know like the back of your hand. Alpha Centauri or Super Mario 3 would be my own choices.

I'm playing kotor 2 right now and if you can get past the jank and some of the sillier bits it's a great reminder of why it's a classic. Would play the first but can't be buggered getting it to work when I believe the remake is on the way.

Any of the old school Tony hawk's games also fill this role for me, especially Pro skater 1-3 (I never really vibed with the open world stuff in the later games).

Or of course whatever kind of extended rpg suits you. The PlayStation or PS2 final fantasy games are obvious contenders, or maybe some of the cooler western RPGs (which I have never been particularly big on so no suggestions).

But really it's hard to say without knowing what you like and what you played as a kid.

Pizza Tower, it's wario land + sonic + saturday morning cartoons

Terraria, Rain World, batMUD, Redout 1 & 2, Kirby's Air Ride emulated in Dolphinkart for that sicc ass online no shared screen play, Caves of Qud, Sword of the Sea, Hylics 1 & 2, Animal Well, Nightmare Kart, literally just Sonic Adventure 2 Battle on steam or emulated, Swords and Sandals Classic Edition, Kenshi, Narito Boy, Heroes of Hammerwatch, Outward (feels like a passion project but also old school rpg with co-op), Death the Kidd, Star Garden: The Trial (another kirby air ride), and Hellpoint

All of tjese games I listed except for KIrby Airide with dolphin kart can be played singleplayer. Some are only singleplayer.

Demon Tides came out recently and had me doing exactly what you're describing lol. It's a stylish platformer about overthrowing a king - good messaging, but also pretty silly too. The open world is a a series of islands that you swim between by transforming into a snake. It's a great game.

(There is some parental trauma if that is a deal breaker)

Also, have you considered Diablo 4? I just finished it with my gf and we both thoroughly enjoyed it.

Gregtech New Horizons

Ultrakill, best shooter I have played in a while, very fast, doom feels slow after playing ultrakill

Yakuza 0, its quite long and the best yakuza overall, many crazy story misions mixed with many stupid side quests, the bad thing is japanese weird sexual stuff is quite common

Do you like strategy? I can play a single game of civilization 4 (with chronicles of mankind mod) or 6 for a whole day if i have the time

Maybe victoria 3 for a more grand strategy and rising revolutions

Hotline miami 1 and 2, fast paced top down shooter, quite hard, one hit kill and revive loops, the best soundtrack ive heard in my life

Celeste amazing platformer, it has some trauma talk about anxiety, but you can skip it if you just wanna play

Outer wilds for a more relaxed and exploratory game, not as adictive tho, its more like a puzzle game about discovering secrets but its magical

Deep Rock Galactic, coop shooter, Rock and Stone!

Slay the spire 2 just came out, roguelike deck builder

Tropico 4 my favorite city builder

You can pirate most of these except the ones with multiplayer like DeepRock

I would give Path of Exile 2 a try if you liked Diablo.

I'm not sure whether you're looking for games that bring back childhood nostalgia or if you just want games with the same cognitive load as Diablo 3. Regardless, I would highly recommend jumping into the Roguelike genre. Many games in the genre are modeled after games we played as kids, but with twists.

Roguelikes/Roguelites/Games with Rogue Elements

• If you ever played Diablo 1 or Diablo 2 and want more of those games, Halls of Torment is a good one.
• If you played side-scroller beat 'em ups as a kid, Absolum is a good time.
• FTL: Faster Than Light is an OG in the genre and holds up to this day. It's largely a spaceship management game with text-based RPG elements.
• Brotato is one of the few of these games that I've 100%. It's a great game to play while listening to podcasts or music.
• If you like card games or deck-building Balatro and Slay the Spire are incredible.
• Risk of Rain 2 is one of my favorite games of all time. It's a third person shooter with a mysterious, sci-fi setting. If you'd rather play a side-scroller, Risk of Rain Returns is the remake of the original and is also fantastic. Both have the same arcade-y feel that you likely enjoyed with D3.
• It's already been mentioned, but both Hades 1 and Hades 2 are fantastic.
• Crab Champions is an underrated shooter
• Heroes of Hammerwatch II has already been mentioned, but it has similarities to Diablo
• Into the Breach is a great tactics game
• Returnal is an awesome third person shooter
• If you ever played Geometry Wars, I can't recommend Sektori enough
• Vampire Survivors - most people have heard of this one
• Glyphica is a typing game

Some honorable mentions that aren't really roguelikes but are still fantastic, laid-back games:

• Tetris Effect
• Lumines Arise
• Bro Force
• Dredge
• Katamari games
• Spritfarer
• Superflight
• Need for Speed Unbound reminds me of Need for Speed Underground of my childhood. It's got cringey dialog, but the gameplay is good.

Some older games

• Descent 2 - Doom, but in a space ship basically.
• Diablo 2 Resurrected - IMO better than Diablo 3, but YMMV
• Baldur's Gate Dark Alliance - Surprisingly decent ARPG that I played on gamecube as a kid
• Starcraft 1, Starcraft Broodwar and Starcraft 2 campaigns
• Pokemon, as some suggested. I would recommend just starting at the beginning with red, blue or yellow. They're probably dated at this point, but I'm sure they hold up.
• SSX Tricky and SSX 3 are awesome snowboarding games that can be emulated on PC
• Pokemon Puzzle League - lesser known, but addictive tetris-like game
• Pokemon Pinball - one of my favorite pinball games
• Pokemon Snap - Chill game where you take pictures of Pokemon
• Super Monkey Ball - you're a monkey in a ball that has to navigate obstacle courses by moving the world around you
• Honestly, just look up the best games that you never played for systems during your childhood at emulate them. The PS2 alone has thousands of hours of RPGs that are some of the best of all time (shadow of the colossus,

• Vampire Survivors, Deep Rock Galactic: Survivor, Soulstone Survivors or Halls of Torment are great horde survivor-like games (I think they're their own genre now)
• Cult of the Lamb, just really funny and incredibly polished, interesting genre mix between a Binding of Isaac-like roguelite action game and a simple but fun construction and population management game. It sounds weird but it works so well.

Wouldn't recommend Path of Exile (2?) to any casual Diablo player though. Play Path of Exile (2?) only if you generally like Diablo but wished Diablo would be more challenging or have more content or be more hardcore. Diablo is already a time sink and can be played in a hardcore way but PoE is just "advanced Diablo" in almost every measure, it basically overshadows it completely in terms of scope, challenge and complexity.