Interesting idea for Hexagon grid, smooth movement and controls and props on SDL usage.
Only issue I'd have is that you have very little time right from the begining to make moves, which is hard to get into the swing of it.
Very good game to be made in such a short time, I liked the art a lot and consistant style of the visuals, everything felt smooth and bug free. The game made me need to think of how to manage the cards and I changed how many of good/bad ones I worked with as I went on. Enjoyed it a lot and played till the end. Music was nice, not too intrusive for background music. Difficulty scaling seemed about right.
Only note I would have is that even after reading the instrustions at the bottom, I still dragged things around for a minute or 2 trying to undertand how to hurt the enemies using the Key up top corner but once I got that, the rest made sense. So I would suggest slightly different/more to the tutorial instructions.