A few improvement suggestions: Create a random vector velocity for the bullet shells so its not just landing in the same spot (creates a trail that doesnt look natural at all) PLEASE set a limit for max amount of zombies at a time on the screen. You should not be trying to instantiate 100's of prefabs at a time in the higher rounds. Or at least enable/disable them when outside of a certain range relative to camera space. Other than that, not bad at all and pretty fun!

Game is just awesome for breaktimes in school, work, bus, simple rules, simple gameplay, own highscore so you can write your tag and be the best

Cool to kill some time :D

Awesome game.