The core code is good, but the game needs some tweeking to be funier. For example reload mecanic is really unnecesarry, it should just reload automatically, because there is no point in pressing R, when game could do it for you. Also the anemies and the player could be faster to make the game more fast paced. Also the art is not very good. You should keep your pixel sizes consistent, because now it is very easy to see that art is taken from random places. Anyways, game is quite decent, just needs some tweeking