Felt like an incremental game, with no heavy decision, and still… wait: "Start Wave 18"? No I'm pretty sure I just went for a wave or two…
Good job, mate. Good job :D
Seriously though, I like the idea, I just felt it lack a real strategy making system, Once you connect your towers to every upgrade, there is no more much challenge. Maybe limiting the amount of incoming connections to each tower, or making the number of connection for each an upgrade you could push the player to make more important decision.
Great work!