Like I always say you're God and once again you have proven it this game is insane! I love that you have a grid system and that you make your own nav mesh AI you have such a good future in the game dev industry.
The only problems I found is that you can cheat the system and buy a lot of zombies and then level them up so I would have done the price increase cost go of the amount owned not the level they're. And the audio was a bit loud when attacking from time to time.
Overall it was a great game with pretty particle effects, smooth game mechanics, cool textures and lastly a gloomy atmosphere.