Thank you so much for the detailed feedback.
I agree with pretty much everything you say. The plan was to have a twist on the theme in each level. Things like introducing different blocks and audio each time you progress, to make it more varied.
I would also have loved to do a boss battle at the end of each level, but I ran out of time. The difficulty does increase with each level though.
As for the theme, this is just my interpretation. I was going more for a vibe and a style, with the hearts and the streams you shoot looking like a cardiogram and so on.