I don’t particularly like Hearthstone, but even I have to admit that it’s brilliant in its accessibility, and pretty much the perfect entry point for the genre. Just make sure that if you like it, you try Magic or Artifact or something else more complex before you settle in to one game.
As for Artifact, I’m at the point where I kind of wish I had sold all of my cards initially instead of just the excess. I would have made money off of the game (joining Diablo 3 in that club!), still been able to play the quite-awesome draft mode, and been able to ignore the not-super-fun-right-now constructed mode. I hope that this sticks long enough to get some expansions and really open up the card pool, along with adding some usability, to the point where casual constructed has a bunch of fun (if not meta) decks to play around with.