By all logic, Bioshock 2 should not be this good. Not only is it a sequel, but it's a sequel to a game that really didn't need a sequel. We've seen Rapture, we've fought the splicers, we've had the rug pulled out from beneath our feet and we've seen Ryan's underwater utopia near its end. What else is there to see?
Without creator Ken Levine and the Irrational Games team at the helm there were questions over whether a second dose of Bioshock could measure up to the first. Was it really that cynical to expect a quick and dirty follow-up built to cash-in on the original game's success?
The first few hours don't entirely allay your concerns. The original's opening was unforgettable, from the moment your plane plunged into the sea to your first glimpse of the marvels of Rapture, to your first encounters with plasmids (genetically engineered psionic powers) and the deadly, deranged gangs of splicers.
By comparison, Bioshock 2 feels mysterious but low-key. Sure, you're now an early prototype Big Daddy (the armour-clad ten-ton gorillas of the original game), and you're on a mission to rescue the Little Sister you bonded with many years ago, but the actual experience doesn't seem to differ much from the first game.
The locations, while new, still fit firmly within the style set up by Bioshock - as they should - and, apart from the fact that you can now wield plasmids and conventional weapons simultaneously, the mix of combat and exploration seems mostly unchanged. You've blasted packs of splicers before, hacked turrets and security cameras, used Incinerate to melt ice and experimented with plasmids and passive gene tonics before. What's changed?
Of course, that's not quite fair. There are tweaks and additions everywhere you look. The old hacking mini-game has been replaced by a simpler, less obtrusive timing test at the bottom of the screen. The new weapons - Big Daddy variants of the old machine gun and shotgun - pack a real punch. The drill, which can be used to skewer enemies in a brutal fashion or swung as a last ditch melee weapon, works superbly. The old research camera, where you shot footage of enemies to unearth their weak points, has been streamlined and reworked, and using it will make your life much, much easier as the game goes on.
Plus there are new enemies to battle. The existing splicer types are now joined by a hulking Brute splicer, charging and hurling objects in a bid to bring you down. We get new variants on the iconic Big Daddy, and - best of all - the much-hyped Big Sisters - fast-moving, vicious female versions of the Big Daddy, who hound you relentlessly until either you or they are dead.
Within the first few hours we also see the biggest new feature - a dramatic change to the way you interact with the Little Sisters. It all starts as before, see the Little Sister and her Big Daddy protect her, take down the Daddy, then grab the creepy little girl. Yet now things take a different direction.
While you can still harvest the Little Sister straight away, the more moral alternative is "adoption" - let her guide you to corpses laden with Rapture's miracle juice, Adam, then protect her while she harvests the stuff. As soon as she's at work, the splicers will come thick and fast to get her, so you have your work cut out keeping you (and her) alive. Once she collects her full quota, you can take her off to the nearest vent, where you can harvest or rescue your charge as you wish. The only problem? This sort of behaviour upsets the Big Sisters, and before long you'll have one of them on your tail.
These are big and very tangible changes, yet it's a while before they affect the overall feeling of deja-vu. Everything works - in fact the actual combat is more challenging and satisfying than before - but Rapture seems to have lost some of its power to surprise you. The visuals are often breath-taking, the art design is never less than brilliant, the music and dialogue remains spot on, yet the law of diminishing returns seems to apply. Bioshock 2 is consistently a very good game, but not, you begin to fear, a great one.
Just give it time. With later levels the game settles into a new rhythm. The locations become more eerie, more open, more spectacular. The level designers rediscover the magic of the shock moment, or ways to exploit the twisted beauty of Rapture, or the lunatic behaviour of its denizens.
The more you go on, the more you realise that while the plot remains linear, guiding you from location to location just as the original storyline did, the harvesting stuff - effectively a rolling side-quest - opens up the gameplay, encouraging you to plan ways with which you can protect yourself and your Little Sister, both from the splicers and the Big Sisters that come later. If you like setting traps, finding ingenious ways to use plasmids and looking for a tactical advantage, Bioshock 2 is very much your game.
And when the plot finally kicks into high gear - which it only does late in the game - it's absolutely devastating. Bioshock is rightly celebrated for everything that goes before "Would you kindly?" and (slightly less rightly) pilloried for everything that follows after. Bioshock 2 is almost the opposite, hitting its emotional high-point only as the game nears its conclusion. For the last few hours, Bioshock 2 is simply, undeniably great.
The biggest surprise, however, is that the new multiplayer mode is much, much more than a brainless bolt-on - an underwater Quake with added Plasmids. With levels set in familiar Bioshock locations, it works hard to borrow concepts and mechanics from the single-player campaign. For instance, you can research the corpses of fallen foes for a damage bonus, hack turrets, discover and don a Big Daddy suit, or use the vending machines for health and Eve refills.
The use of persistent characters with a persistent experience system - opening up new weapon and plasmid upgrades - is a stroke of genius, giving you reasons to keep coming back for match after match. I suspect Bioshock 2 multiplayer won't have the longevity of Modern Warfare or Halo 3, but it has enough to it to make a viable alternative for a while.
Stripped of some of the original's shock and awe, Bioshock 2 struggles at first to hit the same heights, but the improved gameplay and an increasingly interesting storyline make it a worthy sequel in the end. If you hated Bioshock it's unlikely that Bioshock 2 will win you over, but this is one of the most atmospheric and compulsive shooters around, and the new multiplayer mode is surprisingly good fun.