Well, great job! This would be amazing as an actual game.
Then, as a comment, it's a little strange that the player is an absolute beast (almost never taking hits, even against bosses... even against the final boss!) in almost all levels and in the Trench of Despair he just mostly sucks and doesn't even try (the boss actually whips his ass). I understand that the idea is to reflect the actual mood of the character, but maybe it would've been better if the level was actually insanely hard and the hits were almost unavoidable (and maybe taking the form regrets or "ghosts" of what he actually wanted/dreamt of) and after those hits he may actually reflect the despair. And also, given that the octopus actually spares his life, maybe he should be like a "mentor" of sorts, guiding him in the right direction. In the other levels, maybe he should've received some hits and regained some health with music related stuff, so that he doesn't come as an insanely good player. Anyways, that's my opinion and suggestion. It was an amazing job all the same.