FANTASTIC idea! I have to say right away that at first I was confused about how things really work, because we get everything right at once and, even with the tutorial at hand, it wasnt very pleasant to read it to figure out exactly what was going on... and I think this is kinda ok, it being a "game-jam game" after all, but there are some quality-of-life improvements that would make a whole lot for the experience (as people already pointed it out).
That said, the game is INCREDIBLE. Its super tactical and smart, and just so damn fun to play. Its also pretty hard, but once I got the hang of it, setting up the defenses and managing everything were very rewarding and I'm amazed that you could make it so well balanced in such short time! Really impressive work.
Audio is very good too and so are the graphics (although the UI have some of the previously mentioned issues). Overall this is an outstanding entry with good ideas implemented skillfully. Congratulations!