The graphical style works really well, it would've been so cool to have some sound effects and music! I really like the wireframe circle that appears if you pick up a tower to show it's range, it's a relatively small detail but it looks super polished and is really clear.
Even though you have a clear explanation in the beginning, it still took me quite some time to figure out exactly what was going on, but once I figured it out I ended up really enjoying the playthrough. Nice job!