Toxic Fog / Radiation damage = Potatoe / Potato in my opinion.
I would not like Radiation either since you cant see it and its just taking pills against a timer. But a toxic Fog would really affect your experience since you can´t see far, dont know which dangers are nearby, zombies can ripple off your connection to the oxygenbottle, you need to drive slow and carefully.
Imagine beeing on a foggy street, bleeding, 20hp left, searching for a shelter to hide and hearing zombies around you but you dont know where they are.