Alternatively, a friend can take over the secondary forces. This is a great way for two players to work together, or for an experienced player to demonstrate the The Art of War in ways Sun Tzu never even considered. With time-travellers, commandos in crop-tops and giant robot monsters. Clearly, he lacked imagination.

Sadly, all this technology comes with a cost – the feeling of connectedness. Playing with a friend is a very different experience to playing with some random player at the other end of the world, and not having distance between members of a team can often create a feeling of distance that you just don't get with a split-screen.

This is also true of deathmatch, but to a lesser level. In competitive gaming, everything's about you, and your score. In co-op, it's supposed to be about 'us'. Not having your teammates there can heavily encourage score chasing and irritation, not support and teamplay.

Shooting 'em up

And yet, there are exceptions. Of all the amazing things that Team Fortress 2 does, top of the list has to be that even now, a year later, people take it in the right spirit – as a funny game, where losing can be as entertaining as winning.

A team with no hope of winning suddenly emerging from their bunker waving shovels instead of flamethrowers, or creating a circle of healing around the final capture point and fighting with the power of positive thinking, cheers everyone up.

The fact that the enemy you're cooperating to destroy is another team of mostly-sentient humans doesn't make a difference – you need someone to fight, and bots will never offer the same opposition as a close-knit team. This is something that RPG games like Warcraft desperately struggle with.

When new content goes live, nobody knows how to deal with it, and the result is lots of killed parties and a massive uphill struggle. However, as soon as tactics emerge, and people know how the bosses respond to X, Y and Z, things become much more mechanical. The attacks may come in a different order, or when you're not ready, but the encounter itself is fixed.

People are less predictable. True, they'll typically gravitate to certain ways of dealing with a situation – most notably the path of least resistance – but there's always a random element that can be impossible to plan for. Just when you think you know what they're doing, you find a couple of turrets placed in exactly the right place.

Dead to rights

Left 4 Dead is easily the most advanced co-operative shooter released so far. While teambased, it's trying to simulate something that would previously have been the sole domain of single-player action.

Its engine is built around creating a narrative flow instead of simply throwing in more monsters, and that's before factoring in another team of players who'll, no doubt, be spending the next year at least engaged in a deep study of evil.

It's particularly unusual for shooters in the way that it focuses on a party as a physical unit, with the name alone reinforcing what a bad time most players will have if they cut off and try and take on the zombies on their own.

The problem that most co-op content faces is one of over-familiarity. There's something about a ten-minute long deathmatch that remains addicting and exciting, even a hundred games later.

Ploughing through the same content in a group, even a good group, quickly loses its shine. People typically don't want to play through a dungeon, like Karazhan, a hundred times; they're simply compelled to in order to gather the rewards. Replaying a single-player game doesn't have that, and most get bored of it quickly.

The same goes for strategy campaigns. When you've finished the book, you don't want to read it every night. And since by that point, the AI's little if any problem, and you know the levels backwards, you may as well just turn the guns on each other and enjoy the far more satisfying challenge of a good scrap against an opponent who can play without cheating.

This doesn't mean that co-op is a failure. It's just a more limited experience, one which requires more of players and burns out faster. Played right, some of the best experiences on the PC are working with someone.

However, without a stream of fresh content to keep the experience new and interesting, playing this way is more likely to be a one-shot experience than most multiplayer modes.

It's no surprise that as people stop gathering around a TV to play games, the odd exception like the Rock Band series notwithstanding, the focus is on more team games and deathmatching.

That's left co-op somewhat out in the cold, but with games like Red Alert 3 and Left 4 Dead to show everyone how much fun it can be, perhaps not for too much longer…

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First published in PC Format, Issue 222

Now read 11 signs you're no longer a hardcore gamer

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