This was a really cool concept! I love the killing cards to activate effects mechanic, very creative! Was also very nicely polished, well done!
I think theres definitely something in your mechanic that you could explore further. I think if you offered some deckbuilding choices like choosing cards, this could work really well.
I'd also recommend putting the enemy's stats above them rather than making the player hover over the enemy to see them, because I found myself forgetting what enemy was most threatening. If I could see it at a glance, that would help.
Overall great game, and I think there's a lot of potential here!