Great game!
Unfortunately I can't figure out how to get past the spiral enemies in sector 6, how to avoid getting hit? The only option I see is using the shield from sector 5.
After many many tries I cleared sector 6 with pure luck. The spiral enemies seem a bit too hard compared to all previous enemies imo.
I noticed in Arcade you can keep scoring in a sector if you miss the last ring. Perhaps it would be better if you stop scoring once you've missed one to prevent milking early sectors for points.
Since it's hard to survive for many sectors in a run starting from sector 1 it be might fun to have a separate leaderboard where you can continue your sector's best score.
I noticed you can easily clear sector 9 by keeping the boss at the top without hitting him.