Free to play card battling game that is beautiful, easy to start playing, and offers a ton of replay-ability.
Pro Near-perfect balance between going first or second
There's no significant first-turn or second-turn advantage in Hearthstone. The player going second gets an extra card from his deck as well as "The Coin", a card that gives one extra mana crystal for one turn. This subverts the advantage that would be gained otherwise by the player going first.
Con Huge Money Sink
Although you can "technically" play for free, Hearthstone is very stingy on rewards. To get the limit of 100 paltry coins free a day, you have to win 30 games vs mostly players who have much better cards than you. It can take a new player 6 to 8(or more) hours to accomplish this. And after all this you get a pack of 5 cards that are often completely worthless to any viable deck. It's possible to get cards like "Angry Chicken"(worthless card) as the "Rare" card several times. You can also get a bunch of cards you already have a lot of.
Con Crafting is expensive
In lieu of trading cards, this game uses a disenchanting/crafting system to handle duplicate copies in your collection and being able to obtain the cards you want. Many cards disenchant for paltry amounts, and the best cards cost lots of "dust" to be able to play with.
Con The reward system is not significant enough
Hearthstone's reward system is very lackluster, providing little to nothing of significance to the casual or excessive player. There will be times when you feel heavily rewarded by the game, but these times are few and far between and if you are driven by rewards you will likely lose attraction to this game quickly.