The game plays really nice and upgrades feel rewarding. There's some really good design with abilities, and it's really amazing that characters have very distinct feel of play. You've managed to make the progression system really rewarding. Also, I didn't realize at first that rerolling gives you all three cards again, I was running with a surplus of crystals at first :)
My only issue is It may be just me, but isometric perspective makes it a bit harder to judge jump distances.