As a CAVE and Touhou fan, I felt right at home. It's been awhile since I've played a proper shmup and this reminded me of why I love them so much. Excellent presentation and music. Also really like how some enemies can only be killed in certain mode.
Two minor critique is although I love the visuals, it is a tiny bit muddied because of the pixelization but my eyes got used to it after a minute or two. And the other is the boss' pattern are a bit too random. I managed to save up a lot of shields to just brute force the boss because I was having trouble figuring out how to weave through it.
Edit: Just downloaded the game instead of the web version and beat the expert run. I didn't think I got the slowdown effect on the boss in the web version doing the novice run, which made the boss much more doable