Find a seat, if you can! Blizzard's Warcraft-inspired free-to-play collectible card game juggernaut Hearthstone has just hit 20 million players... and shows no signs of slowing down.

It's no surprise Hearthstone has become such a hit with people; Blizzard's CCG manages to be familiar to veterans of the genre while still bringing in new ideas and playstyles you couldn't find anywhere else. While many other card games revel in the intricacy of their mechanics, Hearthstone mastered the balance between depth and complexity. Newbies have a fighting chance against experienced vets, but there's still enough over-the-top combinations of cards and abilities that veterans can find something to love. Plus, it's hard to beat Blizzard's pricing structure: the base game is free, and the only thing that costs money are additional packs of cards (which are easy to earn in-game if you're patient), and expansion packs.

Speaking of which, Hearthstone's first major expansion, The Curse of Naxxramas, arrived recently, adding new cards to frustrate and excite players as well as content that's unusual for a CCG: boss fights. Unlike physical card games, Hearthstone has the benefit of being virtual, so adding in AI-controlled opponents is no big deal. Should Blizzard continue supporting Hearthstone with new cards, shiny expansion packs, and brutal boss battles, we foresee people drawing from this deck for a long time to come.