I think its a fun concept but I think the UI should be updated to be a bit more readable/clear so the player can make glance decisions (like here's the card's required energy, here's the grunt energy) better. I also think the main menu could use some work with more obvious buttons rather than the glowing paper. It's a cool aesthetic idea but I got a little lost when I played for the first time.
I know this part will probably take significantly more effort than it's worth if you're not actually planning to have this game updated for any long period but I think having battle animations would make things more visually interesting rather than a static sprite that's being slowly moved. Maybe something basic and all encompassing (like throwing, shooting, punching, blocking and healing) that gets the job done.
anyway yeah i like this game but it could stand some visual improvements