One of the elegances of this game is that there is only one of each tower so you aren't feeling grind fatigue at the late stage because it's all about upgrading the same tower at the sole-spot where it stays, of each type.
Beautifully compact design. And I enjoy the kind of early 90's PC game feel, what was it lords-of-the-realm -one- has this look. And that thing which Sid Meier called "interesting decisions" which comes in when you decide whether to deep-build the gold mines in the back-forty against straight offense power.
Much respect.
Gave you an itch follow, if you like the things on my page(s) consider doing the same.
Cheers
--D