We’ve been singing the praises of Hearthstone for some time now, a collectible card game based on the characters from Blizzard’s World of Warcraft. It’s the kind of refreshing experience that reminds you free-to-play games don’t have to suck. So it’s no surprise that over 20 million people have signed up to try it. Blizzard has been cautiously expanding the game, most recently adding some single player adventures and 30 new cards in an add-on called Curse of Naxxramas. Today our sister site Polygon reported that Hearthstone is planning it’s first true expansion set, with more than 100 news cards.