To be completely honest this game is fun and all but with your next project try to have consistent graphics. MC, the Red Ball, doesn't fit with very smooth zombies and shotgun he wields. I think you should make all main sprites like enemies and MC yourself and use assets from store or from internet for stuff that aren't necessary or are to difficult to make. Shooting zombies is pretty fun but I would add more weapons. Maybe I did't play long enough but there is only the shotgun and kalashnikov is missing. Nonetheless, good job but try to make a list what you must do, should do, could do and won't do (or simply MoSCoW method)