Nice review, I believe it joins what others said before, but putting in in different words and with your development helps me draw the lines of the problems with more precision, so a huge thanks!
The overall "organic" part of the game, the learning of controls and increasing of the difficulty is one of the key points I lack today, imo.
For the music, I agree. I would find it very fun to be able to set the whole mood of your game like changing tracks of a jukebox, and started with this idea with just the main theme. How good would it be to set a new atmosphere (theme, sound, colors and effects) like that? (I know the kind of work it require behind... but I like to dream big)
Thank you :)