Thanks for playing and commenting :)
Yes i played around with shaders and special particle effects the first time in my "dev-history"... my kids loved the flamethrower burning right through the zombies.
Maybe you only killed 20 also cause of the sucking webGL version, i had to reduce the size immensely and that killed the playfeeling. So i also recommend the pc version for another try :) maybe then you will find patient zero :)