I love me a tower defense so I already was having a ton of fun. I think this game has a huge potential to become something more if that's something you wanted to do.
- I like the difficulty of only having one tower ( I think this adds some tension to the game and keeps you active)
-I like how progress feels with the cash flow, what I mean is by the time fire starts coming around you have a water tower ect.
I think most of my gripes with the game comes with the UI, its hard to tell when I am buying a tower/placing a tower. I also found the text on the UI for tower descriptions very small. Along with having scroll bar. I think the text of the towers could have been more consistence to not have colors clash within the UI boxes like how water tower text is blue can make it kind of hard to read on the green.
I really feel what would help with this game a lot is more visual aid with damage. Such as water slows tiles down, maybe they change a color to indicate they are slowed because besides movement speed I wasn't sure if I should be switching to the ice tower a lot of the time.
I do like the potential that is here. I like the idea a lot of taking a mechanic away from the common genre of game by forcing you to stay active and only use one tower at a time, promotes smart decision making and planning ahead. Great work and keep it up!