Wow! I honestly was not expecting such great feedback, and appreciate the effort that went into it. You have some amazing ideas that I could implement. I didn't think about adding a tutorial, but it does make a lot of sense; the same applies with with adding new game mechanics as the game progresses and/or when switching courses.
This would, like you said, create variety for the player instead of feeling like they are playing the same game mechanics over and over for 40+ levels. The only difference I have between courses, or group of levels, is different music & background (and gravity depending on the course). So, I can definitely look into adding some new mechanics to mess around with. I really like your idea about adding some kind of collectable (such as coins as you mentioned) that could be used to change the ball aesthetically, such as the color of the ball and/or hats and such.
I also greatly appreciate any bugs you've found. I've played through and tried to find and squash any bug that I could find prior to releasing it to the public. But, I guess I must have missed a couple or few when play-testing.
I will definitely take your feedback to heart and improve on this prototype.