Great game. I love that you included a tutorial and story. It helped me to understand and appreciate the game better. My favorite part would be the menu design. I like it
My suggestion would be - slowly introduce the players to the enemies and bosses. We could use the first level to teach them how to battle and defeat their enemies. And maybe in level 2, they have just 3 waves of enemies. The idea is to slowly build the tempo.
Please take a look at “Ancient PlanetAncient Planet” -- you can get some ideas from their FTUE.
Overall, great job with your game. I enjoyed the story and I like how the story was tailored around the assets used. Kudos