Hearthstone is one of the oldest digital collectible card games (CCGs) around at this point, and certainly one of the most popular. Blizzard's talent for sanding the corners off of dense, crunchy strategy games makes Hearthstone a great entry point for anyone new to CCGs. The art, voice lines, and humorous descriptions on the cards help add some levity to a genre that often takes itself way too seriously.
Over the last two years Hearthstone has gone through significant changes, removing older card sets from standard play and introducing the "Wild" format where veterans can use all their cards. The developers have also said they don't intend to create any more Adventure expansions, premium add-ons which allowed everyone playing to unlock the same cards. Instead, there will now be three themed card expansions every year which include some Player Versus Environment (PvE) content as a bonus.
The PvE content released so far under this new system has been exceptional, and making it free for all players is a nice olive branch for those who miss the Adventures. But it doesn't wash away the suspicion I get that the game has become much more predatory towards players' wallets, and feels more like a "pay-to-win" CCG than it did in the past. I really don't like the direction the game seems to be taking, but it's so much fun I keep playing anyway. I guess that makes me part of the problem.