Because the game is digital, many of the card effects can be randomized, meaning no two matches ever play out exactly the same as the last. Equal parts devastating frustration and jubilant triumph, Hearthstone takes all the best elements of tabletop CCGs and throws them into a giant number generator to see what comes out the other side. You build a deck of 30 cards using one of 10 different classes (Mage, Shaman, Druid, and more) that you think will have the best chance of beating your opponents. The game is similar to many other CCGs in the same category, such as Magic the Gathering.
Nowadays, it has a small, dedicated fanbase of players all striving to achieve the Legend rank every month, and is still adding new card classes and game modes like the popular Battlegrounds mode.
Hearthstone had a meteoric rise in popularity, hitting more than 100 million total players in 2018.