Read, and be shaken by your shoulders: the open-world zombie game you've probably always wanted exists. It's called Day Z .
It runs as a mod for Arma 2: Combined Operations, in a haunted version of Arma's 225 km² imitation of the Czech Republic, Chernarus. It isn't perfect. The servers are usually full. But it is an incredible adaptation of the things Arma does well: emergent gameplay, making you feel vulnerable and powerful, decision making, managing supplies, and tense teamwork.
Check our our Day Z interview with the mod's creator here.
Actually, it's miraculous that it functions at all. Having pulled out my own hair dealing with Arma's sometimes flaky netcode, it's unbelievable that the game can sustain 500-some AI-controlled zombies and fifty players simultaneously.
Players spawn at one of many pre-set locations with a basic kit: a pistol, flares, some painkillers, some beans, a canteen. Other than that, you're naked: mapless and compassless in one of gaming's biggest environments. Food, equipment, and weapons (including custom weapons like a quiet-firing crossbow) can be found around the game world or from killing other players.
If you die, that character is permanently dead. If you exit a server and rejoin another, you'll resume your most recent character--in the spot and with the gear that you left them. That's Day Z's persistency in a nutshell.
Survival mechanics like food and water intake are layered atop the threat of zombies. There's hunting. You need to take morphine to ignore pain. There's a lot more to tell, but part of the experience is figuring this stuff out for yourself in a brutal setting.
In short: it's scary as hell, full of stealth and surprise, you can't trust anyone, roleplaying is effortless, and you might save the life of someone that sounds like Arnold Schwarzenegger.
On my second life in Day Z, I had an unforgettable experience of anonymous cooperation, not unlike what the PS3 game Journey was lauded for. Minutes into a new character, I spotted someone being chased by a zombie. We were both in the open, along a highway that connects a series of hamlets at the southern part of Chernarus. I rushed in to help him; I didn't think I had much to lose if he betrayed me or the zombie killed us both, and that risk seemed offset by the prospect of gaining a partner. We killed the zombie attacking him, but our gunshots attracted a few more. We settled into a back-to-back formation next to a gate, and used the entrance to bottleneck the zombies.
All through this, I was yelling instructions and directions of zombies. He wasn't talking back. I asked if he wanted to work together; no response. We looted a little, picking up anything the zombies were carrying. I tried not to point my gun at him. I turned my back to him; I wanted to convey that I could be trusted not to spontaneously murder this stranger and take his stuff.
It seemed like he wanted to work together. Calmly, in the middle of the night, we crouch-walked with the sea on our right side. I kept talking to him. “Hey. Don't go that way. Don't go that way, dude! Over here. This house.” He didn't always comply, but he stuck with me, leapfrogging from house to house and tree to tree. I figured he didn't have a microphone, or that his push-to-talk key wasn't bound. Whatever, this was good enough. We were alive. We started throwing flares to signal danger—red bread crumbs for illuminating where we wanted to head.
In a moment of safety, I typed. Seconds later, he finally spoke. He called out over Arma 2's proximity-based voice chat.
Without speaking the same language, we'd worked as a two man team, killed two dozen undead, traveled a few miles east, and silently agreed to help each other survive.
CHKilroy's videos are great representations of the best experiences you can have in Arma and Day Z.
Something Awful 's guide to installation is the best setup guide I can direct you to. Be patient if you're hopping in for the first time--connecting to a server (even when it's hanging at a “Loading” or “Waiting for host” prompt) can take several minutes, and the servers are pretty stuffed at the moment.