Fun little game! really dig how you did your water background. Controls where a bit odd and for some reason I had troubles going down sometimes? not all the time. Or maybe the inverted nature was confusing me...not sure.
Now was it me? or did the jelly fish and fish dance to the music....I stopped and just watched them for a moment, and it looked like they moved back and forth to the music. if not, you the ironic movement timing with the music works really well.
for more Gameboy astethicness. i would try to avoid doing any scaling with your sprites. i had a hard time figuring out what to do with my bubbles but ended up drawing them to the pixel ratio needed.
Definitely could be expanded into something more!