Call of Duty: World at War

"You know? I agree with them," says Heller. "People online shouldn't forgive us because we made an okay game in nine months. As a company, Activision made a decision to only give us nine months. And the consumer should be mad because development teams aren't given enough time to make games. I don't want them to turn around and say, 'You guys did fine with the time you had - good on you! Good effort!' but I would like them to come back and say, 'I'm not going to judge you based on that now that I know what you had to make that game. I'll give you a second chance'."

Perhaps the good thing is that, after all the doubt, Call of Duty: World at War actually looks like redeeming Treyarch's reputation. The press event ties in with the recent beta, as well as showing off the co-op parts of the game. "It's pretty late for a beta," admits Heller, "but what we get from it is a lot of background work - with our network and understanding where the traffic is going back and forth. Stuff we get from the beta may help with the patch, if we end up doing one, but probably more importantly for downloadable content."

The flamethrower throws flames. Truth.

A late beta is an increasing trend - betas becoming the new demos, effectively. Because while the caveat that it's not a real version is always there, people judge them as exactly that. "It's a challenge. There's a tension between it being good enough so the players get excited about the game, and it has to be early enough so it can help us make decisions on the game," says Heller.

The co-op play is the bigger change to the Call of Duty formula. Four-player multiplayer online, with a couple playable in split-screen, is a fundamental difference. I get to play a couple of missions, one from the push into Berlin towards the Reichstag and another in the pacific theatre. On one level, it's familiar - there's always been friends with you in Call of Duty, they just haven't actually been real people - but on another, it changes everything. It doesn't go as far as Gears of War or any of its followers in being heavily co-op specific, but there are multiple routes in certain areas. "We tried a couple of different things," says Heller, "like co-op puzzles where you have to come from this angle, and you have to come from this angle. It just didn't feel like Call of Duty. What we want is the red-shirts on your armies. We wanted them to be your buddies, not just some guy who comes in and dies."

So while we're dealing with a corridor shooter, it's a wider corridor to make room for your comrades. All the levels, bar two, can be played in this way. (One, because it's a sniper mission, and the other because it's the classic on-rails shooter aboard a machinegun-covered Blackcat or Toothrat or Bosscat or something. Which is a kind of plane, apparently).

Otherwise, in basic play, it's just the single-player game with friends. With a few changes. "We do scale up the enemies," says Heller. "That was really where we spent our time, making sure the AI scaled appropriately. So if you go in with four players on veteran [difficulty], it's a really hard game." The addition of the ability to revive fallen comrades - and failing of the level if you don't - completes the basic experience.

But there are other approaches to co-op to bear in mind, like competitive co-op. This is where you play with your friends in the same levels, and compete for scores. "Almost like Geometry Wars, you get multipliers as you get more kills, until you get the ten-times multiplier. And to get to nine and ten times? It's melee kills only. So you can get a score in the millions when your friends are sitting around in the thousands." The obvious comparison is Bizarre Creations' The Club, except with multiple people playing through a level trying to max out their score at once. Yet again, memory plays a large part here, in knowing exactly when to expect enemies to appear so you can get them first.

While it immediately shatters the game's credible atmosphere, it replaces it with something else that seems to be as compelling. "There's a really cool tension, because you're competing and trying to run through the level as fast as possible... but if you die, one of your friends has to revive you, or you all have to go back to the last checkpoint," says Heller. "So if someone dies, what you normally do is dive in there, get all the kills that you can and then revive them, which is worth a score and keeps your multiplier, but you've taken all the kills and he's taken a real penalty."

Japanese hide in trees. Not truth! Only some do, and normally for a good reason.

That's not all, apparently. "There's a secret little co-op thing that'll be unlocked at the end of the game and we're not talking about it yet," Heller smiles. At which point I mention that I saw the word "zombie" on a mode select menu when a game was being demoed to me previously. He laughs. "I believe the word has been leaked, but I can't be on the record about it," he says. "I will say though that it's awesome enough that it's what we play all day. When we have a break, we play that." (Since Heller spoke to us, Treyarch has confirmed that you and up to three friends will be able to fight off zombies, and buy weapons and other defences between waves.)

So what was on the team's mind when it was doing co-op? What was its purpose? "We wanted it to be a gateway to multiplayer," says Heller. "The conventional rule of thumb for Call of Duty is that single-player and multiplayer players are mostly separate. We have players who play in both camps, but they don't really cross over as much as you'd think they would. We think that co-op could be the place for them to meet and have shared experiences."