One of the best games about zombies. But after a while you will start to experience some lag in your game that will gradually become more annoying while you are playing. There are some ways to fix it but it doesn't work at all so i found a way to deal with the lag and the control freeze in a clunky but functional way.
When the lag is starting you can pause the game and the lag will dissapear for a while. But sometimes this will not work due to the control freeze (Control Freeze can affect your keyboard or mouse, it can even affect both at the same time).
When this happens you have to switch windows quickly with Alt + Tab you will need to have a window open (it can be this page) and automatically the game will stop until you click on the game screen. This will fix the control freeze for a while.