Left 4 Dead (8.5 out of 10)

It's amazing how quickly a situation that's completely under control can elevate into one that will cause even the most veteran FPS gamers to panic. In Valve's first-person shooter co-op survival horror it only takes a split second, a slight lapse in concentration, and your four-man team is on the end of a zombie nightmare. I've never played a game that requires such a reliance on your fellow gamers, with your life more often than not in their hands. Left 4 Dead isn't just a great survival horror game; it's the best example of cooperative gaming you're going to find anywhere.

L4D isn't complicated. There's been an outbreak of a virus that turns humans into zombie-like crazed killers (very 28 Days Later) and you must battle to survive long enough to get rescued. Presented as four separate movies, each with the same cast of four characters, you essentially get 90 minute to two-hour chunks of gameplay, each throwing thousands of infected at you, arming you with a small set of weapons and is never the same twice - while the level layouts remain the same, something Valve has named the Director decides what infected to unleash, from where and in what numbers. A corridor of tranquillity in one game may well be the most hellish moment of your gaming life the next time you play.

Each of the four movies is split into zones, with the goal being to reach a safe room that acts as both a checkpoint and way to stock up on ammo, change your weapon and grab some health packs. Health packs in L4D are scarce, with your character only able to carry one at a time, along with a temporary booster in the form of pain killers. The odd health pack can be found throughout each level, but you can go for a long time without seeing any at all. The lack of replenishing health, which has become the norm in modern first-person shooters, is a key design decision, making every health pack count - and who to use them on something that needs to be discussed.

You're able to use your own health pack to heal yourself or a team mate (downed team mates can also be given a temporary 30 per cent health boost if revived from an immobile state without using a health pack), which is something that isn't quite as clean cut as it might seem. During my time playing cooperatively in the office the decision was always fairly simple. If one of us was near death and without a health pack their health become a priority, with one of the group administering a health pack. When playing with randoms online this decision making often factored in other things. During one online game, student Zoey (accompanied by loud mouth Francis, systems analyst Louis and Vietnam vet Bill) wasn't doing her bit for the team, so when she called out for help (in a rather manly voice), having fallen foul of a vicious attack, my two other survivors demanded that I leave her there to bleed out, for fear that I'd take too much of a hit if a rescue was attempted.

I felt conflicted, but they were right. Zoey had been holding us back since the beginning and we only had to survive another five minutes until the boat arrived to take us to safety. My health could be vital in our survival, so I agreed and left her lying on the ground floor of the house we'd found ourselves in, helplessly shooting while immobile on her back. There's absolutely no question that L4D is more fun when played with friends, but playing with randoms online will throw up unique situations that make it a very different experience. Even playing with one or two AI characters changes things considerably, with their will to heal others even when on the brink of death themselves often reaching Samaritan levels of kindness.

A horde of crazed infected would have made for a fun, hugely enjoyable experience, but it's the special enemies that raise L4D to another level. They've been designed with the express purpose of forcing the team to work together, helping one another out. You could survive an attack from standard infected without too much trouble, but these special enemies can completely immobilise you until a friend steps in to help you out.

There are games you want everyone to play, just so they can experience what you've such a good time with, and Left 4 Dead is one of them. It's unlike any other game I've ever played and demonstrates the true power of cooperative gameplay. It's worth noting that the experience is somewhat dulled if played alone, but if you've got online friends or are happy to play with randoms, Left 4 Dead is a game you simply can't pass up. Just make sure you've worked out what you'd do in a zombie outbreak before you start playing, as you won't be able to make anything approaching a sane decision with a screaming witch bearing down on you.