The simplicity of this game goes hand-in-hand with its elegant artistic style!
Only two complaints: one was with a bit of the level design. I could not figure out how to access one of the fireflies no matter how hard I tried; however, you did give more than 100 fireflies in the whole game, so it's a minor issue.
The other complaint I have is how the menus work. There's no clear indication on how to progress them; there's also no down time for the player's inputs, so I accidentally skipped the ending the first time.
But your game was good enough to play multiple times, so amazing job!