I really like the idea of randomized challenges to go through. Feels very fun.
Would be nice to have challenges not repeat, so you can experience all the variety in one go.
I think getting hit requires some audio or visual feedback, like a screenshake, simple animation (either on the player or on the health meter) or even just a simple "beep"-like sound :)
Even though the graphics are very simple, they fit perfectly with the idea and music.
Overall had a fun time playing it. Good job on releasing your game! :)