Nice little game ! I especially liked the musics ! I wish they were a bit longer though :)
Small note: the fact that there can only be one projectile on the screen at a time makes the cooldown variable, which feels a little off in my opinion. This also encourages the player to hug the boss and spam the attack.
The bubble shower at the end is a great idea! It really felt like a reward after the struggle to catch them during the boss fights.
There probably are a few ways in which you could improve the game, but I still enjoyed it as is! Thanks for the experience!