Blizzard announced their first mobile game at PAX East 2013, Hearthstone, which will be a free to play card game for iPad based on their popular Warcraft franchise. Though they were a little gun shy with us as far as recording live gameplay footage goes, I got to play a few rounds and the game's pretty great. There's fully customized deck-building, a lot of familiar game mechanics for those that have played Magic, and plenty of nostalgia for longtime Warcraft fans.
Either player picks a hero, each representing a major class and having their own special ability. There are 9 classes supported right now, which leaves Death Knight and Monk out (for now). Both sides summon minions to attack each other on their turns by playing cards out of their hand and using limited (but ever increasing) resource points. Damage on minions is persistent between turns, so sont worry if you can't kill it in one go.
Games are live multiplayer, so unfortunately no asynchronous play here. My favorite aspect of Hearthstone so far are all of the little touches. For example, you can see which cards your opponent is fiddling with during gameplay. The decorative UI fringe has some light interactivity, such as a launchable catapult, to keep you entertained while your opponent takes their sweet time. There is a time limit on turns though, and you can always heckle them through preprogrammed phrases or live chat if you're playing with an buddy.
The Warcraft guys have dabbled in trading card games in the past, but so far this is looking to be the most promising effort. Keep an eye out for Hearthstone landing sometime this summer.