The completeness of this game is really impressive. I also liked the boss designs, and the timescale when the player gets hit was a great detail. The music was excellent from beginning to end. The level selection menu is really stylish.
I would like the enemy ships and player bullets to stand out more from the background, but I am having a difficult time thinking of a good change to the palette.. usually I would avoid black and grey, but the black background feels like it comes from one of those science class planet posters right now, and that's pretty cool too.
It felt good to have a goal and see the progress rewarded in various ways through the UI, including the ending. Nice work!