Recs.
Updated
Portal 2 is a first person puzzle game from Valve that costs $19.99. It features a single player and co-op campaign with mind bending puzzles.
SpecsUpdate
Pros
Pro Well implemented tools that improve teamwork
In a game that requires perfect timing and teamwork, Portal 2 features many tools to facilitate teamwork. One of the most helpful is a 3-second countdown timer that can be initiated and shown to both players to ensure you launch that portal or jump at the perfect time. In addition, there is a marker that you can place on certain objects for your teammate to see as well as a setting that shows your partner's view super-imposed on the corner of your screen.
Pro Hundreds of hours of user-generated content
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).
Pro 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 weekend. With almost zero replayability, this makes the game feel incredibly short. Luckily, hundreds of hours worth of user-generated content is available.
Cons
Con Unique co-op levels with co-op specific tools
In Portal 2, co-op is a completely different set of puzzles than the single player campaign. Almost all puzzles require a high level of teamwork that will leave you feeling proud of what you have accomplished.
In a game that requires prefect timing and teamwork, Portal 2 features many tools to facilitate teamwork. One of the most helpful is a 3 second countdown timer that can be initiated and shown to both players to insure you launch that portal or jump at the perfect time. In addition, there is a marker that you can place on certain objects for your teammate to see as well as a setting that shows your partners view super-imposed on the corner of your screen.
Con Steep co-op learning curve
Although the single-player campaign features a gradual learning curve, co-op gives no mercy. The puzzles start off hard and only get harder. It is highly recommended that you play through single-player first if you are not familiar with Portal's mechanics.