Recs.
Updated
Portal 2 is a first person puzzle game from Valve. It features a single player and co-op campaign with mind bending puzzles.
SpecsUpdate
Pros
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.
Pro Challenging puzzles that require creative thinking
The game challenges your brain to use portals, cubes and other mechanics in order to solve simple and complex puzzles in interesting ways. Trying to figure out the best placement of entrance and exit portals in order to gain access to (perceived) inaccessible places takes a lot of thought, especially in the later game.
Pro Creates a sense of accomplishment through a high level of teamwork
Co-op multiplayer offers a completely different set of puzzles from the single-player campaign, which keeps things fresh for those that finished the single player campaign. Almost all co-op puzzles require a high level of teamwork, creating a great sense of accomplishment for the players working together.