@yyz Thanks for the thoughtful comment. I agree that many things in the game could be explained better, and we will take note of it for improvements in the future.
About the slow tower, you are right. It does not really fit into the current state of the game. Now that you mentioned it, I realize that having haste tower in the slow tower upgrades is counterintuitive.
The colors actually symbolize the type of damage the tower deals, which honestly, was not well described in the game.
I really like the idea of using hovering tooltips to display information which we were having trouble placing on the screen! The shortcut keys is also a great idea.
The last wave is wave 20. I too, think that the option to continue endlessly would make the game more complete, and it is an interesting idea to consider. I really like many of the great ideas and suggestions you have here, and will definitely be taking them into consideration. Thanks for taking the time to play our game and for your thoughtful feedback!