I'd like to see something that is not zombies. It seems the entire world nowadays is divided between vampires, bash-da-orcz variations of Lord of the Rings, and zombies. Or, gay looking zombie pirates, which is kind of the best of two worlds...

Please do something else. And please don't do vampires.

If you want to do a survival horror game, that's fine, but there must exist other things in the universe than just zombies. Demons, aliens, mad science experiments, dragons, cloned dinosaurs, anything is better. Not like these haven't been done before (there's probably not a single idea that hasn't been done), but at least they've not been beaten to death a million times.
Also, not-zombie-adversaries wouldn't have to be as braindead as a zombie is by definition. They could have cool special powers, which admittedly is hard to justify on a zombie.

Why not something like a cult that wants the world to end and attempt to kill all who don't join their lines? They've built the mother of all bombs, too, and when the last not-cult person is dead, they will use the bomb to destroy the planet. Of course the end of the world is the most sacred moment, which brings you together with The Creator. Therefore all non-believers must be killed before the world can end.
That story would have an interesting twist. You don't want to be killed by them, but you also don't want to hide too well. Since when they think everyone else is dead, they'll press the nuke button, and you lose, too.

Or prisoners. Let's say some incident has caused a large urban area being transformed into a prison. Just like in the "Escape from New York" movie(s). Now they've found a way out and come in hundred thousands to take revenge on everyone outside.
Same thing as a zombie story, except they've got guns and pillow cases filled with soap, they can drive motorcycles, and they aren't zombies.

^This^

What I really hated about DayZ apart from the bugs was the zombie behaviour. Those spatic, zig-zagging, hawk-eyed sprinters... really killed it for me.
I'd like to see some more complex behaviour. Different types of zombies, with fast and aware types being the exception.
"I am legend" types would be pretty cool, you know, thoses that only come out in the dark.

Some kind of alliance system with base building, safe-zones, pvp.

Wha tI want from a Zombie apocalypse simulator:

- To be like NeoScavenger in 3d and in real time.
- To NOT be multiplayer at all, specially MMO.
- To be necessary to wear chemical suits, and avoid all physical contact with zombies.

Crowds, real threatening crowds of humans and zombies and the true spread of panic and confusion. Watching the faces of people shift from being unsure and unsettled, to worry, to panic then to horror and true fear and flight. Dynamic true sim of group fear during a disaster. If this is meant to be a simulator then this is the angle you should explore, navigating the chaos of panicked dangerous people. Capturing the emotional distress of the masses and the true disaster of the chaos these masses create. Zombies aren't scary, people are scary. Zombies (like all monsters) just show a side of people that we can't escape.

I disagree with this being something other then a zombie game however if its suppose to be a simulation, then zombies should be just another part of what is the real survival during this type of apocalyptic outbreak. Since the real threat is surviving each other. Finding ways to survive together (this is why walking dead is so go).

The book World WarZ explores the idea of people losing their mind and believing that they are zombies and how dangerous they are because although they can feel pain they have full mobility these are proper running zombies.