The coins for example don't really play in much to your final score, and if I recall the game doesn't remember them like it remembers the depth you traveled, which is used as your high-score, I would use them to, for example, purchase a gun to start the level with during the next play-through or somehow add to your final score. Weapon drops are governed by RNG so it wouldn't do much to hurt balancing. as far as the art goes, personally I prefer less solid colors and large shapes, it feels sort of south-park like, that's just my personal opinion. I think it works just fine for this game. I do enjoy your color pallet though, and overall I think it's a great game!