Thank your for your detailed feedback! This is really helpful.
Good to hear the game evoked the good feeling of having others supporting you. With the main menu I was not sure, so nice you liked it.
Yes, in a polished and extended version the sound plays an important role. So your idea of synchronising it on the beat of the nearest bar is something I will look into. I have to check if there is any algorithm which finds it. And more "feeling evoking effects", like particles etc. are good.