Hearthstone

This is a collectible card game from Blizzard, the good folks behind Diablo and World of Warcraft. Like any Blizzard game, Hearthstone is tons of fun on the surface, with vivid graphics and sound effects, but it's also richly strategic. You can create decks for dueling other players using nine character classes like Warrior, Mage, or Shaman. Over time, you'll collect new and sometimes rare cards that will give you a strategic edge.

Extra packs of cards cost money, but you don't need to spend a cent to get the most out of this game. You're guaranteed to get hooked.