Blizzard is a company that has made many succesful titles in the past, like World Of Warcraft, and the Starcraft series. So they decided, why don't take a shot at creating a dumbed-down version of Pokemon and somehow make it competitively viable... and free?
Well it worked. The game has since launch recieved much popularity and gained quite a bit of attention in the eSports scene.
hearthstone's slogan, "Deceptively Simple, Insanely Fun" is not to be taken lightly. In my experience the game was easy to learn but hard to master (I'm still quite bad at it). It literally took me about 15 minutes to get the jist of the game and about an hour before I felt somewhat confident playing others.
Speaking of playing others, the multiplayer experience in the game so far has been phenominal. I have never in one case been paired up against an opponent of far greater skill level and advanced cards. Battles have mostly been fair and to the wire (sorry CS, but hearthstone has a better matchmaking system).
The AI in the game when you are playing in practice mode has also been great. It always seemed to me as challenging but not overwhelmingly hard. It seems to be balanced beautifully for the newcomer so they can learn the basic game.
On the topic of learning, the tutorial system seems to again impress me. As I went through the tutorial, it always felt as if I were in control of the game, not the game instructor telling and forcing me what to do. I felt free to do what I wanted to with the guided instruction of a narrator.
It's Free2Play, but don't get the wrong idea.