Even though I am not the biggest fan of free-to-play, I can acknowledge when it seems to have been done right. And thus far in my playing, Blizzard’s Hearthstone seems to have hit the right balance. A watered down version of Magic: The Gathering it may be, but that actually is one of the reasons I enjoy it so much. Hearthstone makes it easy to jump in and learn the ropes fast, and since the game tries to match you to another player of roughly equal skill, there is no fear of being crushed so completely in your beginning matches.
This game was clearly made with tablets in mind, and the digital realm. It still manages to encompass the feeling of playing a physical collectible card game and a quick look in the store reveals it could very easily cost as much (or more).
I have not progressed terribly far in terms of ranks and the Arena does have a little bit of a paywall: you get in with gold so in theory you don’t have to actually use your own money if you win enough.
If one has access to a PC, Mac, or iPad, and one enjoys playing cards I would suggest giving it a try. That is one of the undeniable perks of free-to-play: no money down!