For those of you who, unfortunately, may not know, Portal was a game released by Valve in 2008. While it is technically a FPS, there is only one "gun" in the game, and that's a Portal Gun. The game is purely puzzle in nature. The star of the game is a woman named Chell, who has the misfortune of being a human lab rat for a company called Aperature Science. Still, for a science company, one has to wonder where all the scientists are... Well, you'll just have to play the game to discover that for yourself. If you haven't yet played Portal, it's only $10 on Steam. It's more than worth it.
Portal 2 takes place many years after the first. Chell wakes up in a Long-term Relaxation Chamber to find that the complex has become invaded by nature. The complex still manages to barely function as intended. GLADOS is also once again awake and she is not happy to see you at all. The puzzles are bigger and harder than ever before. The game is full of bonuses and Easter Eggs just waiting to be found. It also has a full-lengthed co-op campaign with its own story, starring two quirky robots.