Wow, this really is a great game. Though maybe going textless in a 64x64 resolution window might have been a bold choice, I could actually understand what I'm doing which - with these limitations - is quite impressive. Also, after the 10th defeated enemy, just no more cards appear so I'm guessing that is the end of the game. Overall for a first project, this is really amazing.
Also, love the way you implemented the grid system. It looks very clean and readable :)
(Sidenote: If you hover the cursor in the bottom pixel of the cards, the card will pop up and down. Just a small visual bug, but I thought I'd share it just in case)