Really really really hard, I'm not so good at bullet hells but this is probably harder than anything in Jamestown below Judgement.
And the first two phases are probably harder than the rest of the game !
Don't really like that the boss just dies by himself as positioning yourself to be able to hit it makes the game significantly harder.
Very nice graphic touch. love the ship designs and the rain/ether trails really take you into the game.
I really really like the music sync. It's what really made the game enjoyable for me. Good job on the composition also ! It's been stuck in my head for the last two days.
Overall this is very very solid for a 3-days solo project and I wish you'd make a full level of this :)