Solid core design! I like the UI work, though I don't see much reason to put away my cards. I did not know what the discard button was for too. I did run into a couple bugs, such as the hand not updating with new card graphics when I pressed draw, and a pretty major bug where the Draw timer froze and I couldn't get new cards. I was still able to win after that, funnily enough, since stacking towers is so strong and I don't see a reason not to do it.
Suggestions if you expand on this:
In these games where you have a player character moving alongside the towers, I'd always hope that the player can actually attack or contribute in some way. I can also see totems and enemies having various elemental strengths and weaknesses, and the towers potentially combining special effects when stacked on each other.
It's very playable even despite the hiccups, which I think is a great victory. Great work on your first jam project, and I hope to see more!