This is a greeaaaaat and funny game, I just think some polished details would make a great experience.
Some that have come to my mind is that it could have gestures to cast the cards, as in most card games. I know this is a little bit fast paced, but I thought it was kind of intuitive that you could drag the cards to cast them.
Also enemies could give some more explicit clues that they are about to attack, I kind of got the timing on some enemies, but I didn't feel I was getting "skilled" at the game by getting their movesets, I felt I only got to get the timing of more common enemies just for the time I thought they taken to attack.
Also I think you don't need to explain all of your interface, it's quite good and I felt the beginning of the game had a little too much explanation of things that didn't really need to be explained, not at least at the first glance of the game.
At last, I think the difficulty could increase significantly if you made the game more "easy" in terms of gameplay.
I hope this is not taken as criticism, I just really liked the game and felt like this little details could make it better.