First off, the patterns on the dragon boss are amazing! So fun, creative and beautiful, and they’re a test of your observation and creativity rather than quick reflexes. The sprites are beautiful. What I’m really missing is some indication that you’re actually hitting the boss. Some sound effects would be nice, maybe even flash the parts of the boss that are vulnerable. Better feedback to the player means you can do even more interesting things, like specific weak spots. You already have sound cues for at least some of the boss attacks, which is good.
In summary: Fun and very polished game, but needs work on player feedback.