My poor spacebar, I really got into this. Haha. For learning a new game engine on the fly, this game is a 5/5! Also after the first playthrough it seemed the zombies moved faster right off the bat rather than after 5 or 6 killed. Future implements? Uhh you could add maybe some base building mechanics or maybe other survivors can join you as a sort of "turret" system. Whether you build on this or turn it into an entirely different game, great job!