Civlization 5, from Firaxis and Sid Meier

I'm a longtime fan of Sid Meier's games and the Civilization series specifically. No surprise in my mind that the latest game is quite good.

How:

Buy it from Amazon, or Steam.

What:
Turn based, deep strategy, timeless classic computer game. Guide your country from the Stone age through the Internet age, seeking to achieve dominance through diplomacy, culture, might or science.

Who:
Play Civ 5 if you like turn-based strategy, resource management, simulation and replayability. Play if you want to conquer the world, learn a wee bit of history, and see what happens when the Maya drop a nuke on the Assyrians in 2012 and then land on Alpha Centauri to win!

Where:
On your Mac or Windows computer.

Why:
The Civilization games offer very high replayability, with each culture (whether Assyria, Maya, Venice) providing different quirks, benefits and special abilities. Combine that with random maps, new opponents, scenarios and variable difficulty, and you can easily pour many days (and late nights) into these games. I'm having a blast with Civ 5 and the expansions: Gods & Kings as well as Brave New World.