In 2007, Valve Software's Portal wowed gamers and critics alike, becoming a surprise smash hit (with almost four million copies sold to date). The video game centers around a wordless protagonist who — take a deep breath — must navigate out of a maze-like facility by solving complex puzzles with the help of a space-shifting "portal gun," all while weathering insults from a snarky artificial-intelligence system named GLaDOS. In the new sequel, you're trapped once again. Only this time, the exit strategy is far more complex — and GLaDOS is even meaner. (Watch a trailer for the game.) So far, critical reaction has been almost universally rapturous. What makes this game so impressive?

Its craftmanship is stunning: Portal 2 "represents the medium at its very best," says Tom Hoggins at The Telegraph. It's a "work of masterful craft, mechanically constructed with military precision, artistically wrapped in a tremendous story and environment." The sequel introduces a raft of "mind-bending" new features, yet every element of Portal 2 has been carefully devised to entertain veterans and newcomers alike; perhaps the most impressive thing of all is that Portal 2's achievements "feel effortless."
"Portal 2 review"

It's delightfully iconoclastic: "Portal 2 is about as good as a video game can be in the year 2011," says Ryan Kuo at The Wall Street Journal, and iconoclasm is a big part of the sequel's charm. The Valve team skewers science, corporate advertising, and even the "Are video games art?" debate. And they manage to do it all with the "panache and sprightly wit of a Pixar film." This game "constantly subverts and toys with your expectations" — in extremely enjoyable fashion.
"Portal 2 is a hole in one"

And it's also hilarious: The best thing about the first Portal game, says Evan Narcisse at TIME," was the commentary it made on highly structured corporatism, like a stripped-down sci-fi cousin to Office Space." Portal 2 doesn't aim for the same target, but is generally "jokier, chattier and a bit more mean-spirited" than its predecessor. The insults hurled at players by GLaDOS' are more pleasingly caustic than ever, and two new characters — one a  "bumbling hyper-verbal robot eyeball named Wheatley," voiced by Stephen Merchant of The Office fame — are great additions.  All this adds up to "arguably the best comedy entertainment video games have yet produced."
"Portal 2: Our first perfect 10"