You can also set up a timer that counts down from three, allowing you to tell your robotic friend where and when to throw a switch or fire a portal. It's an effective tool for illustrating your strategy. This is done with the 'F' button on the PC, and it operates almost like a laser pointer when you're using the function. In a quick second you can place two temporary icons wherever you please, letting your buddy know exactly where to shoot his portals to get you where you need to go. It could have been a tricky thing to help your buddy know where and when to fire his portal gun, but the game gives you the ability to point to a place on a wall and place an icon there, drawing the attention of the other player.

It works so well that voice chat is almost unnecessary. What's amazing about the co-op mode isn't that it exists and is a very good time-although both of those things are good news for gamers-it's that Valve has created a mode that gives you a bunch of innovative tools to work together. This standalone campaign stars a duo of robots called Atlas and P-Body who have to work together to solve all the puzzles, each with his own Portal gun. The single-player game can take six to 10 hours to play, and the co-op campaign is at least five hours long. There have been many complaints about the length of Portal 2 but, like many of the complaints leveled at the game, they're mostly unfounded.

Portal 2 coop level 2