This is my kind of tower defense! Love the idea, and the way each tower controls differently. Not sure if it was intentional, but I did not like how the bow behaved if I started holding down the button too early from the last shot - once ready, instead of charging the arrow from where I clicked, it started charging/aiming from where my mouse was at the instant it became ready which felt unnatural to work around.
A few ideas that I think would feel nice, but you can take or leave: have keys to cycle between the different weapon types so you aren't clicking on a button for them, or have each available at the same time but on different towers. I know your theming was as the last remaining tower, but I think it would have played just as well if I didn't need to wait for an animation to swap items and could directly pick one of x towers to fire.
Really liked it, well done :)