Hey, great game! Had a great time playing it, trying to beat my highscore.
Not sure what is the relation to the theme, but the graphics were very pleasuring and the game was fun to play. In my opinion though, you should add a cooldown mechanic to the gun, it felt pretty cheesy beeing able to just rapidfire my way out of bad situations.
The coins also had no meaning, I guess you planed some sort of shop but didn't get the time to do it? Upgrates would be pretty fun as well, always giving a feeling of progression.
Pretty good overall, one of the bests i've seen so far. Congrats :)