It's well executed, well polished, and from what I can tell well balanced as well (so many wells, lol).
I felt a little like my actions didn't really have much consequence as the game played out: I would eventually beat the boss as long as I just kept hitting the button to buy either thing. Having said that, it did feel good to see the cards grow in strength and the in-game feedback was great both visually and mechanically so there are definite merits to the design.