Multiplayer will not become an addition in a later patch, unfortunately; Undead Labs has confirmed this themselves. Hopefully, modders will find a way to include this into the game at a later point in time.
As for the game itself, I've spent 30+ hours in it, and I'm still having fun with it. Combat's solid, survival's fun, loot is both randomised and found in realistic places (i.e. you aren't going to find a rucksack full of ammunition in a medicine container), and the missions themselves can be fun too. I wouldn't say it's a game for everyone though, you may want to consider looking at some gameplay footage and/or taking a look at some reviews.
But they will have the Sandbox DLC though, so thats not too bad.
Still MP would have made this game awesome. Guess they couldn't figure out how to do it in a large map scale.
On SP it will only show zombies in the vicinity you are in, on MP it would have to be everywhere on the map which could be a resource hogger.
[Edited by DABhand, 9/25/2013 12:23:34 PM]
They actually claimed that the whole idea was to have some type of multiplayer but the one thing holding them back was the time it will take to implement. So it's possible, just not feasible. We should see it in their MMO though, based off State of Decay. I'm not sure but I think it's called Class 4.
Edit: NVM...read their announcement. Apparently they meant "co-op" multiplayer instead of "MMO" multiplayer.
"As many of you know, we had originally planned to offer co-op multiplayer in State of Decay. However, we had to make the decision to cut it during development, which we announced in our forums one year ago."
"We want to see a multiplayer State of Decay as badly as you do, but itís not feasible to retrofit it into the existing game. That said, I can say definitively that multiplayer will be the absolute heart of any future State of Decay games."