A neat concept!
pros:
I liked the music changing along with the scenery!
cons:
- I went back to level 1 after dying at level 2, more punishing than expected.
- The bullets went through my character at times and was unsure how close i needed to be to attack without getting hit i could get to enemies at times. perhaps add a shadow to the hitboxes of entities? bullets also went through some scenery and stopped at others.