The concept is really interesting and well executed, although a few improvements could be made. I think adding a kind of "brush" tool to spawn more units at once would make the game feel much better to play. Also, the ram has too much health in my opinion, making it too easy to win. A thing to consider if you're going to work on the game post-jam is making the font bigger, so that people with worse eyesight can read the unit descriptions.
I liked the level design. It was also really satysfying to watch my units destroy the enemy fortifications. I would love to see this idea built up on some more. Good job on the game!