To be honest, it's one of the best GB homebrew games I've played in my entire life. I love the cutscenes, the artwork, the font...
The only thing that I think could be improved is the intro song, it only uses one channel, maybe you could add a little bassline or a very soft White Noise H in the fourth channel to make a quiet drumline, for example:
C-4 28 - - C15
C00
I would love to see another version with more levels in the future.