A 1:1 scale world is unrealistic. A better idea would be to have a couple of different places that are large areas, but self contained. You could have New York, for example, and not just the city; you can do a bit of countryside as well to create the varied environments.

I like the interaction between players. They're forced to work together.

There are some things I don't like though. Logging out, really, shouldn't leave you in danger. Imagine having something come up in your life only to find you've been killed and have to start over. What a pain!

Along with that, the fact that players become boss zombies upon death. If you play for ages and then quit, your character will just be an epic pain to new players. Imagine if a wave of people just quit playing; any newbies would find themselves screwed. Of course in your psycho huge world that would be easily avoidable.

Oh, and I don't pass out after 20 hours awake. I understand that it would be unreasonable for anyone to play that long but still, don't be too restrictive

Your concept is fantastic. The only way I could improve it is to make it one of those virtual reality gizmoes. Because who wouldn't love to experience a zombie apocalypse and be able to go "oh it's okay my friends and family aren't dead" after it!

I also applaud the sheer effort you went to. I mean jesus h christ that's a lot of text.