I know the theme wasn't really incorporated, so I'll ignore that for my comment.
It was a really neat game! It had great compatibility, nice pixel art/visuals, the audio was awesome as well. The only bad thing would be innovation- I mean, the art is good and everything, but the idea is just a normal platformer. To be fair, it is underwater at least in this demo. It just wasn't incredibly unique.
Other than the theme and innovation, it was an amazing game! :D