Hmm, this really feels nice. At first it feels creepy, then it just transitions to something that's rather calming. If I were to put in video game terms, it feels like I'm in some kind of dungeon or something. [specifically a water-themed dungeon] There's nothing much to criticize here, except somewhere around 2:02 to 2:15 feels rather off-key, and I don't know if you did it on purpose or not, but I think it ruins the feeling a little bit. Also just a suggestion, maybe you can also extend the ending a little bit, like add an effect where the music box would just turn off or something, like a reiteration of the beginning, to give it some minor details. Overall, I kind of like this experimental song you made here. Hope your friend feels the same too!
P.S. What was the sample/soundfont you used for the music box? I really want to know. :0