I like the economy of getting coins to later spend for different actions. It does seem that leveling up is almost too easy though. Of course, it means that you will have less card draw and less warriors in the Training Area, but you'll receive more coins each turn which might make up for that.
Some really cool choices about when to level up and how to upgrade your warriors. And how your warriors get stronger and stronger as the game progresses. If your training area is full and you lose a 3 star warrior do they go back to the supply or can you swap them with a lower level warrior in the training area so that that one gets discarded. It would be pretty painful if you spend a few turns improving a warrior only to lose him when you have no space left.
Really creative ideas here and cool mechanics!