Treyarch is under more pressure than any other developer right now. The phenomenal success of Modern Warfare has taken the Call of Duty series, as well as the entire FPS genre, to another level. World at War now has to cope with not only meeting the lofty expectations of fans, but exceeding them. Not only that, but the developer has a job on winning over a sceptical fan base, many of whom have bemoaned the return to a WWII setting and lament the fact that it's not being made by Infinity Ward. And people say the Prime Minister's job is a tough one at the moment.

Of course it's unfair to say that World at War is simply CoD4 in a WWII skin, but at times it does feel like that. It's built using Infinity Ward's incredible Modern Warfare engine, and so has an unavoidable familiarity. Left trigger to zoom, right trigger to fire, click the right thumb stick to melee, click the left thumb stick to sprint - it's all in there. There's a perk system that works in much the same way (one of our favourite new perks sees a pack savage dogs hilariously descend on your enemies) and those familiar and satisfying yellow points pop up above your victim's head, too. Yes, the weapons are different - they're less powerful and you won't find any laser dots, no matter how high you climb the level cap (this is World War II baby, it just wouldn't make sense) - and there's some tank driving and shooting, but for all intents and purposes, World at War is Modern Warfare minus about 70 years.

So, why bother then? For us the game is exciting because of the hugely entertaining four-player campaign co-op (four-player online, or two-player local split-screen), a game mode that we're sure will convince Modern Combat veterans to put down their air strikes and pick up a flame thrower, even if it's just for a week. Here there are two options - normal play and competitive scoring mode, which adds a dash of competitiveness to proceedings. At a recent preview event in London we got together with three other game journalists to blast our way through Blowtorch & Corkscrew, a level senior producer Noah Heller (expect an interview with Noah next week) described as one of the hardest levels World at War has to offer. And so it proved.

The level is so named because of the real world tactics Allied troops used against the Japanese in World War II. They would burn the long Okinawa grass with flame throwers inch by inch, weeding out the Japanese troops hidden underneath traps and in trees. It was a painstakingly slow process, but one that had to be employed, if you didn't want to be surprised by a bayonet to the face.

Impressively, this is actually how the level plays out. We began with player one (player one is always Private Miller of the US Army, the rest assuming the roles of other non story-based soldiers) taking hold of the flame thrower and torching the grass as we inched towards our target - Wana Ridge. Soon enough, camouflaged Japanese troops popped out of the ground, screaming Japanese battle cries as they head straight for us. Things got very busy very quickly - more Japanese troops flanked us from a hill to the east and soon enough we were taking heavy damage, red markers showing where the hits are coming from. For us it was a scramble for cover, but for player one it was a different story. Spraying everything that moved with pyro death, he sat back and watched the yellow bonus score multipliers pop up all over his screen. The weapon made him feel invincible, he told us. We'd say the flame thrower might be a bit overpowered, but then we were covering his ass from a distance. Without that kind of support you're going to get chewed up by the Japanese horde in the blink of an eye, because of the weapon's short range. This, as they say, is proper team work.

One of the big questions we had going into the four player co-op was what kind of challenge the game would present four decent shooter players. This was something we felt Halo 3 suffered from - even on Legendary difficulty four players are able to breeze through most of the game. Treyarch's answer is to increase the number of soldiers you'll face, rather than change the hit points or accuracy of individual AI. At times during Blowtorch & Corkscrew it felt as if hundreds of Japanese descended on our position. With four of us hammering our way through the level, the game threw as many bad guys as it could handle. And, despite the fact that we were playing an unfinished build of the game, we didn't notice any slowdown, which is great news from a technical standpoint.

After dealing with the initial wave of Japanese, the next objective was to sort out an MG holed up in a bunker on a raised bit of land. He was protected by what felt like an army of troops, which is great for campaign scoring potential point of view but not so great from a staying alive point of view. It was here, under heavy fire from the MG, that we experienced World at War's revive system. When you take enough damage the screen will go black and white and you'll be forced to sit down and take pot shots with your pistol. If left alone long enough you'll bleed to death and fail the mission for everybody (an embarrassing feeling to be sure). That is unless one of your buddies comes along and revives you by jabbing you with a magical syringe, triggered by holding down X on the 360 pad (the version tested) for about two seconds. The great thing about this is that you're motivated to stop killing bad guys and revive your buddies. One, everyone needs to stay alive to prevent a fail and a reload from the last checkpoint. And two, if you have the campaign scoring on, reviving gets you 400 points - a hell of a lot in the context of the rest of the game. That the game slaps a big revive arrow on the HUD, pointing you in the direction of your bleeding mate, makes it all the easier to sniff them out and save their ass.

Multiplayer does feel like CoD4 with a WW2 skin, but that's not such a bad thing.

After sorting out the MG (via many revives - thanks guys!) the next objective was to destroy three heavily manned bunkers marked on our mini-map nearby. You might think that without communication we would have separated and spread our attack across the three objectives, but all four of us naturally gravitated to the same bunker at the same time, which is a testament to the quality of the level design. One by one we assaulted them, slowly working our way through the waves of Japanese soldiers, one player using the flame thrower, the others providing support from behind. Kamikaze Japanese soldiers who prefer to charge at you with bayonets than retreat do make you jump, especially when clearing out tunnels built into the hillside. Once the bunkers are cleared, you have to chuck a satchel charge inside (press left on the d-pad to select then press left trigger to throw) and detonate from a safe distance (with the right trigger). With the three bunkers sorted it was on to a final bunker, manned by a number of MGs. Weeding out every bad guy was a slow but intense process, and a dangerous one at that. The fire from the flame thrower damages friendlies as well as enemies, and it's often a difficult job not flaming your co-op buddies by accident (when you shoot a squad mate you get a minus to your score). And the Japanese troops themselves are very well disguised, making it hard to spot them in the tall grass. This isn't something we're complaining about, it's just one of the many reasons why the level is quite hard - and we were only playing it on the regular difficulty level.

It's great fun though, and something World at War can brag about in the battle with Modern Combat for gamers' hearts and minds. The competitive scoring adds a great deal to proceedings, and at the end of each level you'll get a leaderboard which shows who's top dog. Yes Blowtorch & Corkscrew plays out much like a level from Modern Combat, with spectacular scripted elements coupled with intense fire fights, but doing it with three friends is, frankly, better.

With the open beta in full swing the focus is squarely aimed at World at War's multiplayer. But we've got one eye on the campaign co-op too. For us, it's this feature that could convince Treyarch's critics that the developer's got what it takes to surpass the brilliance of Modern Warfare. You heard it here first.

Call of Duty: World at War is due out for Xbox 360, PS3, PC, PS2 and Nintendo DS on November 14.