The game idea is intersting, but could use some extra work. Right now, most of the healthbar feels pointless (roughly past the point of the total damage of your and your opponent's highest damaging cards). baiaooo did have some suggestions in his comment, but I'm going to add maybe playing around with the card mechanic a bit more. Like, maybe you only have 3 cards in your hand, and those you've played won't come back until you've exhausted your deck?
I enjoyed the deckbuilding aspect, which also meant that the order you fought the enemies in mattered, as a card you can get from one enemy might be really helpful against another.