This game is great! Definitely the best shmup on Playdate so far, and certainly the most complete. The graphics are top-notch. I would totally pay for a sequel/longer version with more stages and lives/checkpoints/powerups. (Like, $9.99 for a version with 5 levels or so)
I personally think the enemies have too much health -- I think with more enemies with less health each (and more firepower for the player) you could get some REALLY exciting action going on. Also, if you die during the boss, the boss music continues playing when you restart the game and the playdate crashes.
As it is it works great as a memorizer/puzzle kind of shooter, but I think you've got the framework for something amazing here.