Nice job! Definitely a goofy experience but there's something there. I had a little bit of trouble getting myself into the right position (you might want to make sure your camera is in the right place in your build and check the "Floor Level" vs "Eye Level" Setting. Also, I know I had to play a lot with the physics settings to get my game (which is also physics based) to work at a small scale. Might be worth taking a look at that too.
But it works! I'd love to see more defense in there eventually. But its a great start!