Cool concept! I like the idea of having to conserve your resources when you go thru the dungeon. The How to Play was reasonably effective, but I wish the controls were shown too because I didn't know the arrow keys did anything until I died a few times.
I think this game has a lot of potential! My suggestions for making the game slightly more strategic is that you can see the pool of cards that every enemy can choose from, similar to how all of your cards are displayed. This might not be in line with how you want to design the game and the choice is ultimately up to you, I am just giving ideas
I also think that it should show how many cards an enemy has left somewhere, so you can gage better whether you want to engage the enemy.
I feel like having less cards in your deck would be an improvement, because it would mean you have less cards you have to sift through and you have to be more conservative with your resources. And the dungeon sizes would need to be shrunken to accomodate, or you could pick up card packs to regenerate your cards.
Overall well done, fun game concept!