What Portal 2 is
Portal 2 is a first-person puzzle game set in the Aperture Science Labs. You move through test chambers, solve problems with the portal gun, and deal with GLaDOS, the computer companion from the first game. The single-player campaign brings in new characters, new puzzle mechanics, and a much larger run of test chambers than the original, plus areas of the facility you have not seen before. The physics are central to the puzzles: portals, momentum, and the various chamber tools combine into challenges that are inventive rather than simply punishing.
Playing it together
The two-player co-op mode is a separate campaign with its own story, its own test chambers, and two characters that do not appear in the single-player run. It is built around shared problem-solving: both players need to place portals, move objects, and time their actions as a pair, and the puzzles ask you to coordinate your thinking, not just split up the work. Co-op runs online, and Shared/Split Screen Co-op lets two people play on one screen. There is also Remote Play Together, along with Remote Play on phone, tablet, and TV, so someone on a different device can join in.
Building your own puzzles
The Perpetual Testing Initiative lets you design co-op puzzles and hand them to your friends, so the levels you play do not have to stop at what ships with the game. The Portal 2 editing tools are included, and Steam Workshop support means shared creations can be picked up directly in game. Commentary is available in case you want to hear how the chambers were put together.
Before you start
The single-player and co-op campaigns are separate, so two people starting co-op together begin fresh rather than replaying the story. Controller support is full, with DualShock and DualSense controllers covered, and captions are available if you want them. Camera Comfort, custom volume controls, and playable-without-timed-input options are there if the default settings do not suit you. Saves can be made anytime, and Steam Cloud carries them across. The tags list it as a platformer, puzzle, and comedy game as much as an action one, which fits the tone: the writing and GLaDOS keep things light while the chambers stay genuinely devious.