The frisbee/boomerang projectiles were great and I loved that I had cover to hide behind.
The pacing felt a little off - sometimes I'd be waiting a long time for new enemies to appear, or for the dialogue to continue. Sometimes the dialogue would continue before I'd read it. This would be a simple fix with spawning new enemies once the previous wave was dead and progressing the dialogue with a mouse click.
I also noticed that some graphics were scaled oddly - you should be able to fix this to turn off antialiasing in future builds, it'll make your art look much crisper.
I was really surprised by the boss fight - I wasn't expecting it at all! It was a great challenge and I managed to survive just with one health left! Really had my palms sweating. Excellent bullet hell gameplay.