Thank you for playing and giving me a feedback, I am glad you had fun playing it.
You need to build cages to have more prisoners, I think I mentioned it in tutorial. I should add it in to cage's description, I don't know why I never didn't.
I am surprised you managed to complete most levels without upgrading. I am afraid as developer I didn't thought much about how player might play. Clearly I'll need to overview stats and functions of some towers. Idea behind fire tower was that it's attacks put enemy on fire, dealing periodic damage thus even enemies out side of its range could die to a fire damage.
Thank you for a video. Explanation provided in it was pretty good and examples of games that used such orthogonal design were clearly inspiring. I Hope I'll be able use that concept to make game better.