This game is very elegant and enjoyable. A nice twist on the Spire-like mechanic. The card effects are all pretty clean.

There's a bug in the web version (I don't install games that I can play in a browser):

* When I come back to the game after shutting my computer down, my progress isn't saved. 

Possible improvements for gameplay:

* It would be nice to be able to see what new enemies will appear next turn, and how many are left in total for this battle.
  - There's definitely room for this information onscreen.

* When you've reached the exit, and there are no enemies left, "End turn" should exit the battle.

* It's a bit weird that a card counts towards your hand limit while you are playing it. 
  - I played the card that returns a weapon to hand, with seven cards in hand. I expected there to be room in my hand for the weapon after playing the card, but instead I just lost the weapon!

A balance issue:

* You can currently farm bosses for loot drops (and gold?) by killing indefinitely many minions. 
  - I suggest putting a cap on how many loot bags can be dropped in a single battle.