Gwent is free (and a considerable download!) with in-app purchases. Sometimes, you'll need to take a loss to preserve your deck for the next round, a tactic I'm quite fond of.
You can attack your opponent and deplete their point pool by destroying their cards. You earn points by playing cards, each with its own point value. The player who wins two games is victorious. Instead, your goal is to score the most points at the end of a round. Unlike Hearthstone, you don't have a health pool to deplete. Gwent has you choosing from different decks, each with its own abilities and weaknesses. I loved Gwent when it was but a mere mini-game in The Witcher 3: Wild Hunt now that it finally landed on Android, I couldn't be happier. If you've read some of my other roundups, you knew this one was coming! Gwent is my absolute favorite card game on Android, mostly because I'm a massive fan of The Witcher universe.