I agree that this would benefit a lot from some animations. Even some basic jiggly movement or particles when an attack strikes or when a defense is used would bump this up quite a bit. It doesn't need to be complicated or anything. You've already got all the systems in place for the game, so you're most of the way there. I would also make the defense cost some amount of energy because as it is now, you can just defend the entire game to win.
Nice job overall!