The game feels really nice, and its really cute and adorable. Though i have some suggestions.
1. On the third level, maybe make is more obvious that you need to press the lever and hit it.2. Make it more obvious that you can double jump when you have stars, and can shoot when you have stars.
3. Really don't like the pillars on level 4. They basically obstruct the view of the player and it kinda makes the level a bit more frustrating for no reason.
4. Level 4 feels way too hard and frustrating, the part i got stuck on was when I had to break the blocks to get to the lever. I kept on getting killed by the wall enemies, and when I did kill them, the flying enemy respawned and killed me.
5. Flying enemy feels too hard to kill. Maybe make it so that it can only fly in one direction at a time.
6. Maybe add crouching? You can move while you crouch maybe, but go slower.
Game was very challenging, really good game.