HearthStone is the new game Blizzard is working on hard. A virtual collectible card game based on different classes and skills of Azeroth heros, with possibility to use real money for faster advancement int the game.
And as being a closed beta tester, I say it is turning into a fine game indeed. It has truly a World of Warcraft feel in it: graphics, sounds, and atmosphere, without dragging the MMORPG parts into the game at all.
For a casual player, it feels best played against your real life friends, than random world players. It remains to be seen will there wether be any crossover with the parent game like: pets, vanity items, even titles – or not?