Recs.
Updated
Portal 2 is a first person puzzle game with a humorous story and endearing characters. The gameplay focuses on solving fun and well designed puzzles, by placing adjoined portals with your portal gun.
SpecsUpdate
Pros
Pro Co-op does not punish when you want to goof off with or troll the other player
While Portal 2 requires focus and logic, it does not punish players for causing a bit of mischief. The instant respawn system means trolling your friend will affect almost nothing in the game, as there are no in-game setbacks when you die. Being able to stop at any point in the game to just goof around is great for releasing some steam, even when it is at the expense of your co-op partner.
Pro Huge selection of user-generated content that should appeal to any use-case
The game has more than 60,000 co-op puzzles created by users through the Steam Workshop and through mods. Because it is user-generated content, the quality and size of these puzzles vary widely, including everything from simple, one-off chambers to full-fledged expansions with high-quality stories, voice-overs, and new gameplay elements (for example, Mel). By having such a selection of content, there should be something that appeals to just about anything someone is looking for.
Cons
Con Main co-op campaign is short
The co-op campaign in Portal 2 is about 4 hours long for experienced players, meaning it could be beaten in a just a couple days. With almost zero replayability, this makes the game feel incredibly short. Luckily, hundreds of hours of user-generated content is available.