Really great game. A few crashes here and there when there's a lot of cards being drawn and refreshed. It's like a better version of a solitaire game. Obviously you can add more cards which increase complexity, which will require tougher challenges. Another way would be to have this be the game in a meta game. So add a procedural world of places to mine with their own requirements or hazards for each round, and have winning/losing these places have meta consequences. From there you can pretty much take it in any direction.