Personally, I would enjoy this game more if It didn't simply feel like Rock Paper Scissors. As much as the art of game is cool, It would be better if there was some strategy in the way the cards are played, more than just "how lucky can I get"
If you were going to update this game in the future, I would recommend adding a card draft system, where you could create your own deck, and have that deck run through the dungeon. It would give a larger sense of control throughout the game, and create a larger attachment to the cards.
The other option would be to give cards special effects, similar to a normal card game, where for example, one card may have low attack itself, but it multiplies the other card's attack by two. That way, if you draw that low attack card, you still have a chance of winning if your opponent draws bigger than you.