I don't really like that procedural generation video. I mean, one spray of bullets destroying entire walls? Gah! I know this is a game with zombies, but I want beliviablity!
I am a veteran of Urban Dead, a Zombie Apoc MMORPG, and thus has been exposed to many non-Romeo canon stuff. I trust Meph will reject these suggestions, because TMBWS is a bad idea. However, I must list them anyway.
---Zombies have an organized hiearchy, and coordinate their attack times so as to overwhealm defenders. They prepare their forces, and then strike when ready, in order to defeat the enemies. Zombies are outnumbered constanly, and are more powerful tactically than surviviors. Zombies are motiviated by "Barhah", the zombie sense of community.
---Survivors have access to Revivication, which they can use to revive their allies. This means that death is not a problem for surviviors. All newly-dead zombies are alerted to the nearest revive point, so that they can wait to be revived by surviviors. Many surviviors have came up with a new idea called "Combat Revivification" which is basically reviving zombies. Since revives automatically turn zombies into humans, combat revives prove to be an effective counter to zombies, being more effienct than actually killing them.
***There are also Revive Point Killers, humans who attack Revive Points and kill zombies, so as to gain experience. RPKs are hated by surviviors.
***Pro-Zombie Zombies may seek to clog revive points by posing as a zombie looking for a revive, but secretly have immunity to the revivication in quesion. This causes the Revivers to waste time (as well as a revive needle), forcing humans to dispatch a time to kill off the Pro-Zombie Zombie and keep the revive point running.
---Zombies who have been Combat Revived may seek to join back with their Zombie fellows, but wish to bring revenge on the Humans who have taken them away from the Horde. These Zombies are called "Death Cultists", and they will kill as many humans as possible before getting killed themselves and turning into a zombie. Death Cultists are often times more powerful than zombies themselves, mostly because Death Cultists have no qualms about using guns. Meanwhile, in a seperate but related trends, "Life Cultists" start to appear, former humans who decide to kill zombies while being zombies themselves. "Life Cultists" are pro-human zombies, and "Death Cultists" are pro-zombie humans.
---Zombies can have power struggles and ideological struggles. The main ideological struggle within Zombiedom is if "Death Cultism" is in fact fitting in the spirit of "Barhah"? Are you really helping the zombie cause by being a human being and killing other human beings? Or are you in fact implictly implying that Humans are better than Zombies? Sadly, zombies never actually kill other zombies as a result of ideological disagreements and power struggles. They do argue a lot.
---Zombies can never die. They may get headshot, but they'll eventually regenerate and come back to life. Combined with the fact that Surviviors can never truly stay dead (since they'll just revive)...and the Zombie Apoc will remain an Apoc for, well, ever.