It's not often in gaming that being outside in a large pastoral setting can inspire abject terror with every step taken.

After all, in most modern military shooters, players almost always have the benefit of a team to back them up. There's objectives, linear paths, easy-to-use guns, and handy tooltips designed to allow even newcomers to feel like they're part of the action.

None of these exist in Kiwi Dean "Rocket" Hall's wildly popular Arma II mod, DayZ. On July 9th, the mod had 420,000 players. In just over two weeks, that number has more than doubled to 848,000 players.

Plenty of other games manage the haunting desperation of a post-apocalyptic world infested with disease-ridden enemies; DayZ does at times seem a bit like Left 4 Dead tempered with Fallout 3, perhaps sprinkled with a bit of Thief and any selection from id's back catalogue. But for sheer isolation and fear, there's little that come close.

Washed up on a beach in the fictional post-Soviet country of Chernarus, each player starts with meagre survival supplies and a backpack for additional storage. Until a recent update, gamers could look forward to a gun from the outset, however this has now been removed and all players start unarmed.

For new subscribers, the first few hours consist of a lot of crawling and dying. Icons for noise and visibility show exactly how vulnerable a survivor is, as both work together to alert any nearby zombies. Only by crouching, going prone or avoiding any line-of-sight can a player be almost completely safe from detection, which is the most pressing priority given that without any kind of weapon, any zombie aggravation will likely spell death.

E3: DayZ screenshots

The penalty for death is hardcore in the extreme; a complete inventory reset and removal back to a random spawn point somewhere on the coast. The game doesn't discern; grizzled fighter or newbie, once death occurs, all progress is lost.

Swapping to a different server won't make any difference here either – each character, and their inventory, stats and location are saved remotely, and therefore are persistent across all servers. Once a horde is angered, there's no escape other than to fight it out and hope for the best. Occasionally players may be able to sprint to escape a few enemies, or break line-of-sight by circling a few buildings, but more often than not this type of exposure simply allows more zombies to join the meal.

It's not only the recently undead that can be a source of fairly swift death. DayZ is an online-only game, and each server can have dozens of other human players attempting to survive in precisely the same manner as each other. This often results in multiple player-versus-player showdowns, the ultimate goal of which is to loot survival items from corpses. Some players will take this altogether too seriously by creating baited traps to entice unsuspecting survivors, so even finding good loot isn't always a positive thing.

E3: DayZ screenshots

However, it's loot that provides the impetus to continue playing. Most buildings are merely filler, placed in order to provide a convincing simulation. But every so often, some will contain items essential for survival such as weapons, ammunition, food, and utensils.

Cities contain the most items, but also carry with them the most risk. Should a player spent too long crawling through apartment buildings, eventually another survivor will stumble across them, which can conceivably spell death for both concerned.

Rural towns are a good source of supplies, and farmhouse barns can be looted for shotguns and other life-prolonging items. DayZ aims to present the ultimate zombie survival simulation, and to that end, players must eat and drink at regular intervals, so stocking up on food and liquids is paramount.

The health system utilises a fairly rudimentary allocation of blood. Players start DayZ with 12,000 blood units, and upon being attacked by zombies, shot at by other players or merely succumbing to an injury, this total will steadily reduce unless bandages are deployed to stop the blood loss. Should excessive quantities of blood be lost, players can faint for extended periods of time, exposing themselves to further attack. It's also extremely easy to break bones due to fall damage too; such an injury will remove the ability to stand until the correct medical supplies are sourced to fix it.

E3: DayZ screenshots

Any ongoing pain will result in a rapid shaking, making aiming a lot harder. Painkillers can be used to steady a survivor's aim, and heatpacks can be used to reduce the effect of a cold on the player's internal temperature.

The cities within the 225 square-kilometres of Chernarus may be hot spots for player-versus-player combat, but out in the surrounding countryside, zombies are the main threat. By taking to the woods, animals can be killed and eaten in order to survive, and rudimentary campsites can be created to stockpile important inventory items that take up too much space in the range of backpacks available. Eventually, enough parts can be acquired to restore vehicles to working order – jeeps, buses and even helicopters can be used to further terrorise zombies and potential human threats.

The real downside of this mod is the base Arma II engine, particularly when reliability is taken into account. Arma II isn't exactly the easiest of shooters to work with; its many bugs are legendary, and its clunky interface is painful even when the game is running as intended. However DayZ is designed specifically to be unforgiving, and with Arma II's concentration on realism – particularly the range of afflictions each soldier is capable of suffering – it's easy to see why it was chosen.

E3: DayZ screenshots

It helps too that Hall is amongst the staff at Arma II developer Bohemia Interactive, and the studio has worked tirelessly to ensure that nearly one million gamers continue to see the title developed past its current alpha status.

Those wishing to get in on the action will need Arma II and the expansion Arma II Operation Arrowhead, bundled as Arma II: Combined Operations. This pack has shot back into the Steam top ten thanks to DayZ, and developer Bohemia has frequently stated that a standalone title warrants further planning.

Whether or not the future for this mod consists of a full retail release, further interaction with Bohemia's Arma 3 engine, or even a standalone game based on the same concept by a completely different developer, DayZ has already proven that there's a large, dedicated market willing to look past bugs, server glitches and frequent annoyances simply to have the opportunity to test their survival skills in a hostile world.

It could be argued too that game developers who actively pursue a policy of restricting the modding community may look at the success of DayZ and re-evaluate exactly what benefit they derive from such an isolationist approach.

Should that be the case, DayZ may ultimately prove to be far more groundbreaking than the deceptively simple gameplay implies.