Players gained the ability to scale how much zombie strength, speed, and cognition deteriorated as environmental time passed. You could configure a world where zombies started as fast, lethal runners in week one, but decayed into slow, fragile shamblers by month three. Environmental Erosion
To see inside a building, players had to walk up to a window. This significantly increased the tension of looting, as you couldn't scout every room from the street.
The Forgotten Catalyst: Re-evaluating Project Zomboid Build 38