Very cool tower defense game. Love the setting. I died in the second wave my first run.
I’d suggest letting players know which lane will be active so they don’t waste resources defending lanes that aren’t attacking. Maybe start out with only 1 active lane and adding more lanes after the players have gotten a few rounds under their belts.
I’m not sure if it was me or my settings but I had a pretty difficult time getting the timing right. Might want to try out a couple other tempos or widen the bad timing range. Might be able to look at other rhythm based games like BPM, DDR and the such to see what tempos they use for easy, medium and hard difficulties and see if any fits your style.