I really had fun with this game, and I think it's very well done. I blew through the tutorial/instructions, and didn't really read them, but I was still able to figure out what to do pretty quickly. I really liked how many different types of cards there were, as well as the various types of challenges and being able to choose between multiple rewards. Though, I think that when a reward is a card, being able to see what that card does would be helpful to figure out what reward to pick.
One of the problems I noticed was that the balance seems scaled towards being too difficult. I played the game several times, and although I got close to winning, by the time I got there my opposition was too high. I feel like there's a lot of luck involved in winning, which takes the feel of control from the player. Having the opposition increase a bit lower, having more ways to decrease, or even just decreasing the frequency of that as a punishment would be really helpful. Great game!