Nice work and fun concept. Less subtle sound effects, clearer sprites for the bullet and ammo pick ups so they don't blend with the background would help improve the game a bit. Also having added in-game information on the title screen or game screen for pressing R to reload is useful for players who play the game without reading the game page first, of which I'm guilty of sometimes lol. I always find that putting as much in-game information for the player as you can makes your games more enjoyable.