Best Co-op Games Summary:

Deep Rock Galactic

• Affordable, goes on sale often
• Immersive, encourages teamwork
• Challenging FPS; updates are free
• "Deep Rock Galactic is by far the best choice."

Terraria

• Surprisingly deep with much content
• Great for grinding with friends
• "I used to grind the fuck out of it with my bro."

Monster Hunter

• Great for 2 player coop
• Hundreds of hours of gameplay
• "Monster Hunter is great for 2 player coop and can be played for hundreds of hours."

Stardew Valley

• Excellent for coop play
• Offers hundreds of hours of gameplay
• "Stardew Valley"

Satisfactory

• Engaging and satisfying
• "Satisfactory."

Guild Wars 2

• Co-op gameplay available
• "Guildwars 2"

A Way Out

• Unique couch co-op game
• Highly recommended
• Encourages teamwork and competition
• "If you mean couch co op then “A Way Out” is pretty much the only game like that. Highly recommend"

Baldur's Gate 3

• Great co-op multiplayer CRPG
• Divinity Original Sin 2, Remnant From the Ashes, Warframe, and Halo series are recommended for co-op play as well.
• "I would recommend Baldur's Gate 3."

It Takes Two

• Masterpiece for co-op
• Encourages teamwork and communication
• "It Takes Two. masterpiece."

Other Recommendations:

• Overcooked: Best for playing with a friend
• No Man's Sky: Massive, updates regularly, and offers co-op play
• Divinity: Original Sin 1+2: Long games with engaging gameplay
• Warframe: Free hack & slash MMO
• Diablo 3: Co-op play for hours on end
• Resident Evil 5, Resident Evil 6, Nioh, Nioh 2, Stranger of Paradise: Final Fantasy Origin, Returnal, and Bloodborne: Great for co-op gaming.

Additional Mentions:

• Arkham Horror LCG, Tainted Grail, Gloomhaven, Pandemic Legacy, Kingdom Death Monster, Aeon Trespass Odyssey: Recommended for story-based campaign games.
• "I totally recommend Tainted Grail."
• "Gloomhaven is the combat system."
• "Aeon Trespass Odyssey."

Overall, these games offer a mix of immersive storylines, challenging gameplay, long hours of content, and opportunities for teamwork, making them the top choices for the best co-op games according to Reddit comments.