It's a fun puzzle game that's neither too hard nor too easy.
Story: You are Chell, a human test subject, who wakes up to find herself in a hotel room. After you fall asleep, you wake up to find yourself in the same hotel room, except that a lot of time has passed. You're waken up by a sphere shaped robot called Wheatley (brilliantly voiced by Stephen Merchant) who wants to help you escape Aperture Science. I'll stop there to avoid any spoilers. The story is great and the dialogue is really funny. The game also has a lot of surprising twists that make the story better.
Gameplay: The gameplay mainly involves solving puzzles using a gun that creates portals. Portals are like holes that let you travel to different places. None of the puzzles are extremely hard. There are some puzzles that require a lot of thinking but after you solve them, it's extremely satisfying and makes you feel smart.
Sound: This game features some of the best voice acting I've ever heard. Stephen Merchant, J.K. SImmons, and Ellen McLain totally bring the game to life. The sound effects are okay and sound convincing.
Graphics: The graphics are not that bad, but aren't that good either. Some of the environments look great though. One thing that bothered me though, was that when you looked down, it seemed that you were a flying portal gun. You have no legs or a body. I wish Valve worked a bit on that.
Overall: Portal 2 is a solid experience. People who love puzzle games or people who are looking for a challenge should definitely check this put.
Story: 8.8/10
Sound:8.5/10
Graphics:8.3/10
Gameplay:8.4/10
Value:8/10
Overall:8.5/10