Thanks for the kind words, and the very thorough feedback! :D
I'm very glad to hear that we managed to pull off a rhythm game, it's the first time we've done one so there were a few things that were new to us :) Yeah, we felt adding a story was important to help tie all of the scenes together. Without it I think it feels like you're just randomly jumping from one place to the next, which is fine but I think having a narrative helps to drive it a bit more. I think the 'hub' functions in a similar way in that it puts level select and the likes in the game itself instead of just a menu.
Regarding difficulty we always like to try and keep things more on the forgiving side e.g. having pretty wide time windows to hit notes, while still offering a challenge should the player want it e.g. having variable difficulty levels. As you've alluded to, these ideas are also present in the lack of level failures. There are medals that the player can grind for if they wish, but they're never punished if they have a lot of trouble with a particular level (there's even the option to skip it from the pause menu should they want to). The scoring mechanism is also built with these ideas in mind. The player is rewarded with high scores for building combos (which prevents players spamming all the notes and achieving very high scores) but they never lose points for missing, the combo just breaks (so they can still spam if they want to, there's just a slight penalty). Not displaying the missing notes may have been a happy accident though, I can't remember whether that part was intentional haha! XD
Thanks again for the feedback, there's a lot of ideas in there that we'll be able to think about and use in future games! :D
Really glad you enjoyed it :)