Very clever idea for a rhythm game! I love how simple it is! With more song choices, I could easily see this getting super addicting. I also love the UI. The shop icons, currency system and all that is really well developed!!
I don't know if its the game itself or perhaps the graphics causing slight lag, but the sync seemed a little off in the second part of the song where the circles and squares started crossing each other in different directions. This issue fixed itself and seemed a lot more in sync once the holds started. While it's fully possible that it could be my computer being a pain, the sync might still be worth looking into for future development :)
Good job with this. I could totally see this becoming a full game someday!
-Sasha