The art style is really great, although I feel like this game would look even better with some post-processing. I feel like the difficulty is balanced a little too much in the player's favour; a really simple solution would be to increase the number of bullets fired by enemies and to add a cooldown to the player's weaponry. While there is background music (a big plus), I didn't notice any sound effects, which would also be a nice addition. I personally think you implemented the theme fine in this game and I definetely had fun playing it.