At that point the zombies tend to go into a stalemate mode, where they forego normal entertaining zombie tactics for stealth and hesitance. This is where it goes down-hill and things slow down.
The combat really needs to be more rewarding for both sides in order to hold something like this together. As shoddy as it sounds, running an op like this with survivors only using springers would seem to keep things moving.
As for Fort Prince, I think everyone who's been a Zombie out there will agree that the warehouse area needs more cover and concealment opportunities. Survivors love to stand around in there and take advantage of the wide lines of sight.
And finally, an indoor zombie-game needs creepy ambience or music for two reasons:
1. Masking a zombie's movement sound with music greatly levels the playing field.
2. Loud and intimidating music usually makes people more ballsy, and therefore more action takes place.
I'd really like to see another zombie game, they're a blast to play at. They're just so hard to pull together.


