I hit wave 8. I really enjoyed it; but the difficulty does ramp up quite a bit once you reach these levels. I barely have time to finish two sides before dying.
Controls-wise, having it be a drag-and-drop is a bit of a... drag, it would be mercilessly more fun with a drag-and-connect underneath kind of thing - it would make it feel a lot smoother and encourage more multi-track drifting.
I can see some additional complexity with a bit of colour mixing, that seems like a natural way to go.
If the music synced up with when waves started, it would be beautiful. I had a couple moments in my playthroughs like that, but they were coincidences.
I like it! I'll check back for a post-jam version, for sure!