Incredibly addictive and fun... until you hit the wall.
So finally someone has come up with an online equivalent of Magic the Gathering that removes a lot of the unnecessary mental gymnastics while maintaining the strategy of both deck crafting and game play.
Set in the World of Warcraft universe, you take on one of that game's popular character classes, Mage, Rogue, Warrior, Priest, Shaman, etc. and battle it out using minions and spells. The game play is fast (thanks to a built-in turn timer), and of course like all CCGs, you can buy new card packs to give you more options.
That's where the trouble starts. Unlike, say MtG which can put limits on decks (say starter vs. starter only), Hearthstone has no such limits in place. They do allow players to advance without spending money if they are smart and strategic - token 'gold' is awarded based on number of wins. BUT, at least for some character classes, that's only good up to a certain point - once you've leveled into the 20s somewhere you hit the wall, now you're facing other players who've spent money and have very powerful epic level cards that make them practically unbeatable. You still might be able to advance after many, games from people conceding or logging out, but since it takes 2 wins for 10 gold (EDIT: that was a typo, actually it takes 3 wins for 10 gold) and 100 gold to buy a new pack of cards (in which your chance of getting rare epic cards is pretty slim), you might have to play hundreds of games to get past the mid 20s, maybe even 1,000s of games if you're really unlucky and get only packs with cards for other character classes.
Sure, it's a drawback of the pay-for-play system (someone has to pay the game developers, right?), but when faced with spending hundreds of dollars on virtual 'cards' or quitting a hero and grinding a new one, that old monthly WoW subscription doesn't look so bad after all.