Nice adaptation of the theme, really innovative! It's also super impressive that you manage to make such a long rythm game all alone in 48 hours, you can be proud of yourself! I really like the landscape changing gradually as I progress through all the levels, such a nice touch :) The story was a bit silly, I loved it! Going through all the body parts was a bit confusing at first but it really emphasize the "going deeper" concept in my opinion, nice touch!
However, the music at the very beginning of the game was way too loud for me, and too high pitched :/ Also, the first levels were a bit too easy and/or repetitive to me, maybe you could change the pacing of the notes to make these levels more interesting? Having more and more notes was a great idea to increase difficulty, it got quite challenging for me in the last levels! I could not reach the end of the game though, it was getting too long for me D: (I didn't expect it to last this long, super impressive for a game jam game!), I went to the Left Kidney level I believe.
I really like the graphics (felt like vacation!), however I think the keys we had to press did not really match the style of the rest of the game. Maybe changing them to a more "pixellated" version could improve the consistency of your game? Also, I think it would be nice to add some features to add more dynamism during a level, like combo or bonuses, maybe? I'm not that familiar with rythm game in general, sorry I cannot be more precise!
Once again, good job on your entry :)