Left 4 Dead - coming soon for the PC and Xbox 360 - has two things everyone wants:

1) Zombies
2) Co-operative multiplayer

Even more awesomely, these things have been combined by Valve Software – meaning yes, you'll be able to play co-op against zombie hordes on the PC.

Now, gamers have been crying out for co-op PC games since Doom (which, let us not forget, was released in 1993). We've constantly been disappointed with the lack of offerings in this area, suffering excuses of varying degrees of plausibility (although really, the underlying reason was probably pretty simply "it's just too hard and you keep buying our games anyway").

So it was with great surprise that I read the announcements about Left 4 Dead (and while we're on the subject, the new Call of Duty game, which will also be sporting a co-op mode). They did their best to try and dissuade me from being too interested by mentioning it was "by the creators of Counter-Strike", but there's no denying that this title was something I was going to want to check out.

Despite not getting a reply from Valve pre-E3 (well, we only run a couple of Steam Content Servers and have distributed more Valve content in Australian than, dare I say it, everyone else put together, ever since the first releases of Counter-Strike patches that were infamous for destroying the Internet), I managed to sneak into their booth using a combination of extreme stealth, not an insignificant amount of sliding down ropes and slitting throats, liberated Australian army camo face paint, and (probably less significant than the others), the boring expedient of asking the girl at the door if I could go inside.

Upon entry I was greeted with a very rare site at this E3 – actual PCs running games. This was a relief; I was expecting more samples of gameplay on the consoles, so it was a pleasant surprise to walk up to the four screens and see people actually not turning in slow circles and constantly moving the crosshair back and forth and back and forth over the target while the user struggled futilely to aim with the controller, cursing and wishing for a mouse.

I'll come right out and just say what my first impressions were - "is this running in some sort of low quality graphics mode or what?"

My first glance was not hugely encouraging – while the game looked like hella fun, visually it was more reminiscent of Counter-Strike 1.6 – not the new whiz-bang sheer awesomesauce that you would expect from a Source engine game. Your own characters arms and weapons, for example, look low-poly and fairly average, especially when compared to some of the other titles I'd been seeing walking around the show floor.

The character models and the zombies (I should be calling them "Infected", as that is their formal title - but we all know what they really are) look pretty good and the overall visual effect is great though – the level design, while not as intricately detailed as some other titles, still provides a great background for the game.

It's possible that the lower-than-expected quality graphics are one of three things: Just Plain Bad (unlikely), placeholder art (possibly), or an intentional way to make the game perform better on older machines. After playing the game for a while I'm definitely leaning towards the last option – this game is ridiculously fun, and if Valve can hit the sweet spot between awesome next-gen graphics for those with great hardware and good-enough graphics for those with old machines, they are going to sell a lot of copies of this game.

(Please note – I'm not saying the graphics are bad. They're not. The game, visually, looks very good. It's just not as whiz-bang-look-at-me like a lot of other titles we were shown.)

On to the most excellent news – the game is shaping up almost exactly like you would imagine a four player co-op game where you slaughter zombies in such quantities as to almost justify a follow-up title like Left 4 Dead: Corpse Burner.

I played a couple of round of the four player co-op experience in the one part of the game that was being demonstrated and almost had to be dragged kicking and screaming off the PC; suffice to say that it was pretty fun just playing casually with some other randoms, so I suspect playing with a bunch of friends would be really, really cool.

The basic flow of the game is fairly simple – you and your compatriots ("The Survivors") are stuck in the usual situation of being more or less alone with zillions of blood-crazed monsters trying to hunt you down and eat your face. The basic FPS principles apply – there's caches of weapons and health around the place, although the flow of the game is carefully timed such that you tend to move from full-on zombie combat into a period of relative quiet where you can re-arm and heal up before moving into the next stage.

Rather than the Doom-style respawning at the start of the map when you're dead, when you get knocked down by the zombies you can shoot from the ground with your pistol until a teammate can get over to you to revive you (you can actually get swarmed by Infected who will claw at you in a bloody display until your mates can shoot them off you).

However, your health is finite – too many incidents and you're out of the game, so its important to keep an eye on your health supply. Health packs can be picked up and carried around and used as required – although I witnessed at least one incident of a teammate hogging all the health packs, but I guess that sort of selfish behavior is really only likely if you're playing with randoms and/or noobs, so hopefully it won't be that big of a social nightmare.

At least in the part of the game I saw, there's no WMDs, which means there's a strong focus on small arms fire and squad tactics. Lines of fire are pretty important as friendly fire appears to be on by default, which will certainly make things interesting (especially in some of the areas we saw, like narrow air ducts). Pistols, sub-machine guns and shotguns form the base of your kit, and along the way you can pick up some improvements (dual wield is helpful) and some better assault rifles. You can also get Molotov cocktails, which in addition to being effective weapons also have the added bonus of doing so in a way that involves zombies burning and writhing horribly.

There are several different types of zombie – the most prevalent is your basic Infected, which will just charge at you trying to rip your throat out. There's also the big fat Boomer, which will projectile vomit on your face, temporarily blinding you and (as if that wasn't enough) attracting even more regular baddies towards you. Another one I experienced first hand was the Smoker, which shoots out a long tongue to strangle you. There's a few other types as well but I didn't get a chance to see them so I won't bother writing about them; suffice to say there's a variety of Infected with different talents.

It should also be noted that in addition to the co-op mode (which, in case it's not obvious, is what I'm most excited about) there's a deathmatch mode – you can have four people on the side of the Survivors and another four playing some of the various zombie classes. We didn't get a chance to try this out but it sounded pretty cool in a sort of Aliens vs Predator way.

Mod developers have been churning out things like this for a while (like the Zombie Horde mod for Counter-Strike), so it is nice to see commercial game developers taking the hint and putting some serious time and effort into a major title. Left 4 Dead is shaping up to look like a really solid, fun multiplayer game, with a lot of variety and (thanks to some innovations in the way the zombies are spawned) the promise of replayability. I also asked Valve's Doug Lombardi (who was walking us through the game) about modding and he said that it was going to definitely be a big deal for Left 4 Dead, so there's hopefully even more chance for this to stand the test of time.

Valve are in the coveted position of being one of those (sadly very few) PC developers that make new games that you're almost certainly going to have to buy, if only not to be left out when everyone else is talking about it. Hopefully the full game stands up as well as the demo level that we saw at E3 – if it does, then this game will be huge. And then if we're really lucky, maybe it will herald in the new age of co-operative shipping as a standard feature instead of a bold new experiment.

Keep watching for more on this game. You'll probably want to know about it.