I have seen a few tower defense games with only one tower, but this one is my favourite so far, simply because the cooldown is going down even when the tower is not powered anymore. This made the gameplay really fast and it had a good rythm to it. It lacks polishing of course, but thats not what we are here for to judge. With some music that has a nice beat to it and that is synched to the cooldown of the towers this could be tons of fun. Nice work!