Portal 2
On top of being a great game, this physics-based puzzler is also great for your brain. In a recent study, scientists found that people who played the puzzle game from developer Valve performed just as well on intelligence-based tests as those who played popular brain-training apps like Lumosity. Portal 2 is also strangely charming, has a great plotline and boasts the vocal talents of Stephen Merchant and J.K. Simmons, so what have you really got to lose? (PC/Xbox 360/PS3, $19.99, though you can probably find a copy for $5 if you look hard enough.)
