Cool idea, I enjoyed playing. I don't think that the game detects multiple key presses at the same time correctly, which could be related to using something like Input.is_action_just_pressed() instead of Input.is_action_pressed(). Also, it would be a nice change to make the leaves spawn in time to be caught on the beat... Additionally, a difficulty curve could be added to start the player off slowly and build up to the more frantic collection of multiple leaves at the same time.