An endless Tower Defense strategy game. Each level has endless waves where you fight the enemies off until your base is full. Enemies reduce the number of hearts you have at the base when they contact it, once your base is full (out of hearts) the round is over. There are a variety of towers to produce as well as a number of different enemy types to encounter. There is also a permanent upgrade tree where you can spend winnings to increase a number of attributes to give you an edge. You can replay levels you defeated before with your new upgrades, or continue on in the game. During the game each tower can be upgraded with coins (earned from defeating enemies) and they level up. You can set their targeting priority choosing between things like first, last, toughest, weakest (in terms of the enemy defense).
There are a lot of trophies/achievements to unlock as well.