Really cool man! Pretty impressive for your first game, my first game was hardly even playable lol. Main issue I see with yours is that you can sorta just hover over the main boss which makes him harmless because you're out of his line of fire. And I think he spawns attack orbs a bit too common to the point where it becomes impossible at points to avoid his attack. Theres a philosophy in game design that says, "The player of any game should be able to play the whole game without taking any damage" This doesn't mean make your game easy, it just means to give players the chance to play to perfection.
Nontheless though, congrats again on finishing your first game. Welcome to the gang lol! Good work!