Cardstone is a deck building and dungeon game, where you start with a basic deck and a hero (Warrior, Mage, Paladin or Vampire) and then build and improve your deck as you go through the dungeon. After each battle, you have the opportunity to swap one card in your deck with 4 random cards in your card pool. Through this you’ll strengthen your deck to fight stronger dungeon dwellers, but there gameplay is deep because the RNG prevents you from building the same deck every time (although you can make them thematically the same). It is a good premise and I played it daily for awhile. The problem is that the IAP scales really quick – the cost to buy new cards for your card pool with in-game currency grows exponentially. You’ll get a bunch of rare and legendary cards, and a few is better than 0, but the chances you’ll build a deck of strong cards is rare without spending.
The Battle of Polytopia is free and has distilled Civilization down to its core elements, so it’s great if you’re looking to play Civ (assuming you’re OK with isomorphic graphics). The problem for me is that after playing it for a little while, I remembered why I don’t like Civ (troop management and battles). Plus, in this age of mobile games, playing Civ is just too long.