Your imagination's fine? I'm inside the armory of a 3x3 fort complex with a gatehouse entry point, an infirmary, a storehouse, a barracks and an exercise yard. I'm wearing a lab coat and using a lab skill to apply a revival syringe that I found in an office block owned by a mysterioso death-related corporation, and I'm building a barricade to stop zombies from entering the building and attacking me with their claws and infectious bites.
Pop quiz! Am I playing Hell Rising, or Urban Dead?
Jailriot and Shartak show the genre is broader than just copying Urban Dead exactly.