Hearthstone is currently free on the iPad. It's a Collectible Card Game with a World of Warcraft setting. I've tried it and from my initial exploration it's seems to be a decent CCG. Relatively simple, but I enjoy the variety in the characters you can play. Like Magic: The Gathering, it's about trying to kill the enemy character by reducing his health points to zero. You also get to play creatures onto the board, and the creatures fight each other. At the moment it appears to be much less complex than Magic, but it may be because I'm still new so I have not seen many fancy card powers yet. Also I have not explore the deck-building aspect yet at all.