BioShock 2

Sisters are not doing it for themselves. But then, it shouldn't come as a surprise to discover the Big Sister is not the main baddy in BioShock 2 despite what we've been encouraged to think. After all, this is the series that had you take a golf club to its own illusions last time out. If even 2K Marin's press events are a festival of misdirection, surely that's another tick in the "worthy" column for the arch-nerds in the audience.

So who's in charge of Rapture, the underwater city where good ideas go bad? This time it's Dr Sophia Lamb, a clinical psychiatrist and former political rival of Andrew Ryan. 10 years after the events of the first game, she's taken over Rapture to promote her vision of a world where everyone helps one another. It's Lamb who's in charge of the Big Sister, a graceful but unstable and super-violent guardian of the BioShock ecology, whose job it is to keep the gene-enhancing ADAM flowing, and prevent people harvesting or removing the ADAM-collecting Little Sisters from the world.

You, meanwhile, play as a prototype Big Daddy, fighting a typical FPS fight across Rapture to reach the Little Sister to whom you were bonded over a decade ago, back when all this was fields (of cute children plunging syringes into corpses to extract the genetic equivalent of a magic potion). You need ADAM to power yourself up along the way or you simply won't make it, so you'll be harvesting or saving the Little Sisters as you go. Lamb isn't very happy about this which, among other reasons, is why the Big Sister gets all up in your grill. You're her enemy.

Not half as much, however, as somebody else. Andrew Ryan, Rapture's creator and visionary, may be dead, but he's still everywhere you care to look or listen, and his conflict with Lamb is the subject of plenty of the audio recordings you find scattered around the locations you visit. Hardly surprising, since Lamb's collectivist stance is just about diametrically opposed to Ryan's philosophy of rational self-interest. If he were to discover she'd taken over, you imagine he'd be spinning in his grave - providing he could do it on his own terms.

Part of the fun of BioShock has always been that you don't need to get the philosophical stuff to enjoy it, but if you really didn't understand that part of it the first time around, the first section of BioShock 2 that we get to play ought to make things clearer. Ryan Amusements is its name, and it's a series of mechanical dioramas designed to discourage the children of Rapture citizens - born to the city and curious about the world outside - that it's all a bit rubbish up top and they wouldn't like it anyway. It's literally an objectivism funfair.

The kids are all gone now though, so these days it's a stretch of space you need to cross in order to retrieve the Incinerate plasmid - one of the genetic upgrades that allow you to turn people to ice, fire electricity from your hands or, in this case, spout volleys of fire, either to toast your enemies or perform practical services, like de-icing the rails ahead of the train car you were travelling in at the start of the level.

An early highlight is the discovery that hacking is now done "without pausing the simulation", as one developer puts it. You now have a hack 'gun', which can be used directly on safes, doors and vending machines, but also fired at sentry bots and distant switches. Whether near or far, it brings up a little gizmo with green, red and blue zones on it and a needle moving back and forth across them. Press a button when the needle's in a green zone and the hack's successful; press it in blue for a bonus; press it in red to set off an alarm and come under attack, or receive a jolt.

As well as locked doors, naturally Ryan Amusements is also full of splicers, the whacked-out former inhabitants of Rapture who have been pumping themselves with genetic enhancements for over 10 years, and for whom this hasn't worked out terribly well. They also want ADAM, and they certainly don't like you, so they shoot and slash at you on sight (although, as in the first game, it's fun to evade their gaze for a little while and listen in on their tragicomic conversations). Most of the splicers here are familiar.

But there are a lot of them, so it's a good thing you're a nine-foot-tall killing machine in a reinforced fifties diving suit. As a prototype Big Daddy freed from his conditioning, you can splice yourself with plasmids, just like the hero of the first game, and one of the revelations of the sequel is the ability to swap between and utilise them with your left hand while you simultaneously fire regular weapons with your right. Most of the plasmids here are familiar too, although some have been upgraded. Security Command, for example, can now be used to set waypoints for any sentry bots you've hacked.