Thanks for uploading a non-install version.
I liked this game. I love tower defense and this is tower defense in reverse. I played quite a long time (Game Jam games rarely last more than a few minutes for me). I eventually stopped when I was sending a single Goblin out on attack then quickly using Fire to destroy towers. This meant I got an immediate refill and could destroy all the towers before sending a couple of Ogres or shamans in.
You need to remove this loophole, but as a concept of a game I liked it - great job.