Portal 2?

It's not very long, but it has an entire co-op campaign that's completely inaccessible without a 2nd player.

My son and i play weekly. Heres our faves

Deep rock galactic

Helldivers II

Enshrouded

Remnant and remnant II

Valheim

Abiotic Factor has been really fun for my buddy and me. Especially with the new update that came out last week. It's a Half Life themed survival game.

Others that get my vote:

Valheim - Norse mythology themed survival game with Playstationesque graphics

Phasmophobia - THE ghost hunting game(see also Ghost Exile, Ghost Exorcism Inc., Forewarned)

Left 4 Dead - the original Zombie FPS series (see also Back 4 Blood, it's kinda alright) PILLS HERE!

Risk of Rain - Pretty tough shooter series

Stardew Valley - A modern Harvest Moon, farming/life sim

Don't Starve Together - If you played Stardew valley in hell, but everyone's name started with a W

Factorio/Satisfactory - Resource harvesting and logistics sims. One's isometric, ones first person, one has zerg rushes

Grounded - Honey I Shrunk The Kids: the survival game

Deep Rock Galactic - Left 4 Dead for Dwarves. ROCK AND STONE!!!

Overcooked - cooking and serving game, lots of communication required

Portal 2 - First person puzzle game, also lots of communication required

Barotrauma - Submarine sim on Europa, requires marriage levels of communication

Binding of Isaac - Roguelike shooter that's sort of Zelda inspired, multiplayer was a little janky last time I tried it, but that was a while ago

The Forest - Excellent horror survival series

Starbound - Terraria in space

Trine series - A modern Lost Vikings, side scrolling puzzles and platforming

Subnautica 2 - A beautiful and terrifying diving/exploration game, original game has a coop mod 8 years in development, but it's been very buggy

Diablo - First and second games are still very solid experiences and there are some excellent mods out for both

Escape Simulator - Literally an escape room simulator. Has workshop support on steam for even more puzzles.

Green Hell - The Forest, but in the jungle, much more focus on the reality of being stranded in a place where just about everything is likely to kill you.

No Man's Sky - Space/planetary exploration sim

Dead Island - another zombie FPS

Dying Light - a zombie game with parkour

20XX/30XX - Megaman X styled platformers with roguelite elements

GTFO - Extremely hard, stealth based, alien FPS

Most "Souls" games - Very fun coop summoning, if you don't mind the sometimes extreme difficulty

Goat Simulator series - Goofy exploration games

Magicka series - Isometric action adventure games where you combine different elements to cast spells

Barony - a true roguelike FPS RPG, voxel based, very hard

Void Crew - Space sim, mission based, sort of Egyptian mythos themed, meant for up to 4 players but definitely possible with just 2

Human Fall Flat - Puzzle/exploration game

Half Dead series - Cube: the game

Orcs Must Die series - Tower defense

Dungeon Defenders series - also tower defense, but with class based

Secret of Mana - One of the first action JRPGS, the remake has drop in coop just like the original, but I believe it's couch coop, so if you're not right next to each other, you'll need something like Parsec to play it

Have a ton more, but those are the ones I can recall having the most fun. Others have probably listed a bunch of them and I probably missed a few good ones, but hopefully a few of them are new.

You could always tinker with some emulators for some retro coop games!

Since you enjoyed BG3, I'd strongly recommend Divinity: Original Sin 1&2 if you have not played them already.

Other than that, a few random suggestions with sizeable coop campaigns:

• Outriders
• The Ascent
• Remnant 1&2
• Resident Evil 5&6
• Saints Row 3&4
• Trine 1-5
• Valheim

Survival Coop

• ASTRONEER
• Don't Starve Together
• Grounded

Actiony

• BIGFOOT
• Children of Morta
• Content Warning
• Broforce
• Gauntlet
• Generation Zero
• Road Redemption
• Warhammer: Vermintide 2
• Worms Armageddon
• Shadow Warrior 2

Sportish

• Blood Bowl 2

RPGish

• Divinity: Original Sin 2
• For The King
• For The King 2

Strategy

• ENDLESS Legend

Puzzle

• We Were Here
• We Were Here Together
• We Were Here Too

Cozy

• Viscera Cleanup Detail

Co-op is making a comeback!

Playing right now:

• Helldivers 2
• Hunt: Showdown

Ideas based on games you mentioned:

• Divinity 2
• Remnant
• Wasteland 3
• Crayta
• Medieval Dynasty (haven't actually tried coop on this yet, but single player was great)

Interesting team dynamics:

• Deep Rock Galactic
• Lethal Company
• Rimworld (Coop is wild)
• Aliens: Fireteam Elite

Surprisingly Engaging:

• Journey to the Savage Planet
• Golf with Friends

Nintendo:

• Donkey Kong Country 1, 2, and 3
• Contra / Contra 3 (I think there is a new one coming)
• TMNT Turtles in Time (There is a new TMNT already out too)
• Bubble Bobble

Keep coming back to it:

• StarCraft II Coop (free to play now)
• Diablo II Resurrected (still better than III/IV/Last Epoch/Grimm Dawn etc.)
• Portal 2 (lots of challenges to complete)

portal 2

Project Zomboid. Feels like a Sims game with zombie and great survival elements. Arguably, the best zombie survival game to hit the market. Supports split screen couch co-op.

Try out the Divinity Original Sin series, also produced by Larian. Different system and setting but it's wonderful.

i'll just add a few i haven't seen yet:

• Chained Together - running gauntlets while ... chained together
• Children of Morta - adorable graphics meet solid gameplay and vivid storytelling
• Core Keeper - top-down Terraria with great pixel art, full release in a week!
• Cosmoteer: Build your 2d-Spaceship and do what you want! Full workshop support with tons of available mods.
• (hmm so much stuff starting with c, gotta change my game)
• Element TD 2 - classic tower defense experience
• Heavenly Bodies - Adventure game with physics!
• Kingdom: Two Crowns - the right thing for chilling :-)
• Necesse: even more Terraria, but with a huge world and settlements to build and manage. Still in EA, and needs polish, but great game even now!
• Neon Chrome: Cyberpunk twin-stick shooter
• Operation Tango: Asymmetric Coop, one is a hacker, the other is the agent on the ground
• Streets of Rogue: "immersive sim"-top down twin stick action roguelite - i cant even describe it well, but it is heaps of fun and chaos can pop up around every corner!
• Synthetic: twin-stick shooter with tons of guns and a hefty difficulty later on
• Grim Dawn: ARPG, and one of the best in its class. Dated, but still updated (and gets a new expansion soon-ish!). community is running seasons which add new areas, items and whatnot! i've sunk 1500 hours into that one, so i am probably biased when i say give it a whirl.

I haven't seen Rayman Legends mentioned, so I'll throw it out there. It's a pretty flawless game for what it tries to be, and it's a lot of fun to play with a friend. The musical levels are just extraordinarily crafted. Definitely recommended if you're into platforming at all (and even if you're not it's worth a shot!)

Games I enjoyed playing with my then-gilfriend:

• Castle Crashers. 2.5D side scrolling action
• Skyrim Together, although this requires at least one of you to have a decent level of understanding to get things to work smoothly
• ibb & obb, puzzle
• Portal 2, puzzle
• Shadow Puppeteer, puzzle

Remnant 2 and Deep Rock Galactic are the best that come to mind rn.

Remnant 2 is dark souls with guns and coop actually changes the game in some ways to better enable teamwork to make the dream work.

Deep Rock Galactic is just a wonderful little title about space dwarves mining a crazy bug planet. 100% randomly generated. Each of 4 classes feel like they bring something unique to each mission.

Stardew Valley. My wife and I have sunk well over 1000 hours into it and we still aren't bored. The amount of mods for it is insane and gives so much more depth to the game, but vanilla is super well done as well.

Maybe Valheim?

I didn't see these in the list:

Wyldermyth - indie fairly unique story building campaign with turn based tactical combat.

Wastelands 3 - post apocalyptic RPG with good story, choices, and characters. Great tactical turn based combat. Other than the other Larian games this is closest to filling the BG 3 shaped hole.

Halo Master Chief Collection; 1 - 3, Reach, and ODST are amazing co-op. We've played through all of them multiple times. 4 is... disappointing.

You can play Stardew Valley in multiplayer co-op mode, it's also quite cheap at $14, it's available on every platform and even has excellent Linux support

Divinity original sin 1 and 2.

The first one is harder. 2nd one if better to start with. Good fun if you like strategy and storytelling.

I play a lot of couch coop with my kid but adults would enjoy all these too. Most can be found under $20 on Steam and a lot are fairly lightweight games but have good coop mechanics and can be a lot of fun to sit down for an hour or two with.

• Overcooked 1 + 2 (but 2 really is better) you will love or hate it depending on your personalities, nothing in between. We loved it
• Ship of Fools
• Enter the Gungeon
• Lovers in a Dangerous Spacetime
• Moving Out

On Switch

• Cadence of Hyrule
• Don't starve together (only split screen on console not PC... Wtf)
• Pikmin

Og halo was so much fun!

If you're open to silly casual games, Untitled Goose Game

Also, I heard Cult of the Lamb was getting a co-op update

A few I've played with a friend of mine: the We Were Here series, Portal 2, Monster Hunter World, Factorio and Deep Rock Galactic (which we both didn't like, but it's pretty popular)

My wife who is a huge Minecraft fan has been playing stardew valley with me.

She also loves the portal 2 coop

The whole We Were Here series is marvelous. Asymmetrical co-op puzzle games. My friend and I’s recent games list looks very similar to this.

We also do a lot of single player games with one of us streaming over discord. When it’s a slow-burn puzzle or mystery game, it doesn’t really matter who is actually controlling.

For those types, I really recommend Return of the Obra Dinn. We’re currently working our way through the entire Frogwares Sherlock Holmes collection. The old ones are so terrible, which is a greatness all by itself.

Left 4 Dead 2

Earth Defense Force. You can probably get 4.1 on a sale really cheap and that could be a decent introduction to the series as a whole, it also has the best overall story tone in my opinion, made of 110% grade B cheese

If you two enjoy it and don't feel burnt out, you can later get EDF 5, which has several QoL updates compared to 4.1, but tends to have a higher price.

Divinity Original Sin 1 & 2

Edit: Oh, Neverwinter Nights

Elden Ring with the Seamless Co-op mod. It's not difficult or complicated to set up and it works extremely well

Dying Light

Unravel 2

Halo

My wife and I just finished Super Mario Wonder. It was a lot of fun. Every level has a weird psychedelic section that completely changes the players or the level temporarily. It shakes it up and gives a lot more variety than the other side scrolling Mario games.

V Rising - 49.2 Hours

• Online Co-op
• Isometric perspective
• Vampire survival/crafting
• Be a vampire lord with a keep, thralls, blood banks, cast magic, wild shape to a wolf, decorate a castle, posess a horse, make your Castlevania/vampire fantasy come true!

Enshrouded - 123.3 Hours

• Online co-op, 3rd person perspective
• Absolutely beautiful and haunting exploration/survival/crafting/action rpg.
• Early access and already has had large updates
• Wonderful and detailed building system. Will post pics if I remember when I'm at my PC.

Remnant II - 22.5 Hours

• Online co-op, 1st/3rd person
• Soulslike shooter
• Has been quite challenging playing it single player but co-op seems like it could be good with easier progression

Stardew Valley - 252.2 Hours

• 2d Pixel graphics
• Online co-op
• Huge game that has had many updates
• Has been $14.99 since 2016 and will always be $14.99 per the one man developer. All DLC is free and included.

Edit to add: 9 Monkeys of Shaolin - 7.0 Hours

• 2.5D Kung Fu ARPG Brawler
• Open skill system is fun
• It's kung fu. I am not familiar enough with Shaolin staff styles to say if the moves are authentic or not.

A couple titles that deserve mention and I don't see in any other lists:

Children of Mora - Narrative driven action RPG with some light Roguelite-ish elements. Amazing world building and story telling, good character choice/building and gameplay.

Cassette Beasts - Pokemon, if it were good. Much more mature story, tons of quality of life systems that makes building things fun, a weakness system that matters a lot more than "number big" and the entire game is double battles. I've played the game start-to-finish in couch co-op and it was incredible. They've recently added online multiplayer, but I cannot say with 100% certainty that the online allows you to engage with the story together. Couch co-op has one player play as the companion character in an otherwise unchanged experience whereas online has one player character hop into another player characters world.

Weird enough, the Monster Hunter franchise - I'm not sure how this isn't anywhere else in this thread. Use large weapon to hunt large monster. Build bigger weapon to hunt bigger monster. World and Rise are both on sale on Steam right now. World is dumb to move through the story together though, despite the fact that most fans who aren't me are likely to call it the better game.

BattleBlock Theater is a good action platformer that has coop.

Escape Room Simulator is a good 3d puzzle game that can be played coop as well.

Assuming Steam?

• Halo, obviously. Master Chief Collection is pretty cheap to pick up these days, don't miss out on the Halo 3 ODST DLC.

• Ready Or Not can be a challenge with just two people, but it is very rewarding to get a good score.

• Zero Hour is very similar to Ready Or Not, but it has different features and I find it a bit easier.

• Deep Rock Galactic

• Risk of Rain 2

• Elden Ring (Seamless Coop Mod is highly recommended)

• Monster Hunter World (include Iceborn DLC)

• Generation Zero

• Project Zomboid (if you like this one you'll probably sink hundreds of hours into it)

• theHunter Call of the Wild (chill hunting shooter)

• Farming Simulator 2019 (new ones may be better, haven't researched)

• Barotrauma

• Factorio

• Elite Dangerous

• Green Hell

• The Forest

• Sons of the Forest

• Morrowind has an OpenMW fork that supports multiplayer, if you get it set up this can be a fun game to play