If you have never experienced the exquisite terror of five hours of your life mysteriously vanishing, then you should check out Civilization V on Steam this weekend. The game is free to play for everyone until Sunday afternoon, and you can purchase the Game of the Year edition for $12.49, down from its normal $49.99.
The GOTY edition comes with the core game as well as over $40 worth of DLC, including 4 map packs, a bonus Civ (Babylon), the Polynesia and Denmark scenario packs, and the official soundtrack. You can also buy the original retail version of the game for $7.49.