Nuclear war, zombie outbreaks, meteor strikes, economic collapse, alien invasion, no matter how it happens an apocalypse makes for a unique and engaging setting to run a campaign in, even for a jaded GM.
Here’s a few quick tips that can make a good zombie or other post apocalypse game a great one, and keep the group coming back (from the dead?) for more.
No one is allowed to do harm to those of Highest/ Imperial rank, those of the Imperial household or those related within two steps of blood. The second tradition is an executioner must be of a higher rank than those he executes. This leads to "issues" when someone tries to harm a member of the Imperial clan or when these members are subversive. Such people are often killed by the being chained under a giant bell. They die within a day or so from the vibration, but they die untouched by Human hands.