My first thought when I saw the sprites was this: gorilla, zombie, blood. So I think you should definitely rework the readability of the player sprite. Are you working with any color restrictions? The poses also look a little wonky, are these idle sprites or frames of walking animations? Take advantage of the fact that the heads are the most important feature, and it is where the viewers' eye falls first. You could give the zombie some more character by adding an extra skintone or giving him more zombie-ish eyes rather than 2 plain dark dots.