The Idea is amazing, good use of the theme. I would have liked fullscreen and some Audio. I like that you added the feature that the player is falling faster. The graphics are simple nothing too special, i missed some Particles to be honest. Just adding a Particle effect over the whole scene that looks like dust is adding a lot to the visuals. I also think that you shoul have tweaked the settings a bit. I also missed a Screenshake, that gives the bullets more impact. I also wasnt sure how many points i had during play time. A Scorecounter would have helped. Overall i liked the idea you could have tweaked your settings a bit, added some effects and it would turn out great! Good job.