Left 4 Dead 2

Project lead Chet Faliszek tells me the axe can be used to one-hit kill a Witch, if you can successfully sneak up behind her. And it's likely there'll be a dedicated Achievement for that. "If you did that with a frying pan, you're going to have a bad experience," he adds, grinning.

Towards the end of the stage, we're heading down a street, with three-to-four storey blocks on either side. Suddenly, zombies are streaming from top-floor windows in a torrent, before flowing towards us like a slavering tsunami. A great moment.

Reaching the final safehouse proves relatively straightforward in the end. And utterly useless preparation for what comes next. The finale of The Parish is the first example we've seen of 'gauntlet' gameplay, new to the sequel. Starting at one end of a bridge, your party has to make it to the other end, where - a radio message informs you - a rescue helicopter is waiting. There's no holing up and surviving until help arrives. Your mission is literally, and in the best Arnie voice I can muster: "Get to the chopper!"

What plays out is an astonishingly relentless trek down the bridge, clambering over upturned cars and crashed trucks, while crashing waves of zombies burst towards you in a seething, ceaseless flow. There is no respite. There is nowhere to hide. There is only forwards. And if you die, you die. It's up to the remaining party members to push on regardless.

The pile-up of broken motors littering the roadway means that, while the zombies are all coming at you from a narrow, defined space up ahead, their sheer volume means you're under constant threat from those splitting off from the pack to scurry up and down the bridge structure to flank you or box you in from the rear. The closest things to a corner to cower in are open truck containers, which is where to find ammo pickups and the like. But there's very little point in hiding away here other than seizing an opportunity to heal yourself.

One moment sticks in the mind that sums up the frenzy. My character and another had fallen off edges (there are also great holes ripped through the roadway at various points), and were clinging on for dear life, waiting to be dragged to safety by one of the others. Help duly arrived, and, unable to move, I watched with hilarity as endless swarms of zombies kept aborting any attempts to pull us up, until just enough space was cleared before the next onslaught to haul us both up.

It's bloody hard. I don't know what difficulty it was set to, but I didn't see a single group reach the chopper all afternoon. But what a rush.

And that's your lot for now. Valve is promising further substantial reveals of game content in the run-up to launch, in addition to a multiplayer demo that will be made available pre-release. Based on this playthrough, it's more of the same with some neat additions. Which is, again, in no way a bad thing.

The subtleties and depths added by the inclusion of melee weapons, a reworked AI director and so on, won't be fully appreciated until the final game hits. And so, the exasperation of a large number of L4D fans aggrieved that this is being sold as a separate game rather than released as an add-on is likely to continue until people experience it first hand.

Valve simply urges fans to "trust" it; and in fairness the studio hardly has a history of unjustly mugging customers. The various pledges of ongoing support for the original may also prove an emollient, once they materialise (and Faliszek also teases that we haven't seen the last of the original crew: "We love those four, we love their story, but we think there's some other place to go as well. They're not dead, they're still going on. So definitely... We'll see what happens in the future.")