Thank you very much for that detailed feedback :-). Yes you are absolutley right - the music and hearts as indicator is definitively not enough. Also for me (and I should be used to it ^^). Therefor I also thought about colors. I wanted to do it with some PostProcessing-Effects - but I also like the idea of changing the background. At the moment I'm motivated to keep on working on the game so that I can release an update after the jam is finished. If I can keep that motivation then this will be definitively something I'm aiming for.
Yeah the blue AI is more challanging - because of the simplicity behind it. He just have to run away from you. I think here I could increase the horizontal speed of the red cube to help the player. Because atm I think it is too hard.