I am playing BioShock 2 and I am terrified. I am terrified because I know that what I am about to do will cause a horde of Splicers, and perhaps something even worse, to descend upon me and my Little Sister. But, even though I have a choice, I have no choice. I need the ADAM. I need the ADAM to buy new plasmids and gene tonics from a Gatherer's Garden. I need the new plasmids and gene tonics because the game has told me - quite sternly - that without them I'll likely not survive the tough road ahead. So, here I am: a Little Sister on my broad shoulder, a glowing white corpse at my huge, armoured feet, and no real decision to make. I am playing BioShock 2 and I am terrified.

But, I am not defenceless. I am a Big Daddy, for a start, and I can prepare. I can set Rapture against the Splicer horde. With my Rivet Gun, I lay Trap Rivets in a protective circle around my Little Sister. I scout the area for environmental aids: water pools, oil spills, turrets I've hacked, gas canisters I can hurl with telekinesis. I even lay down turrets of my own with the new Hack Tool. I switch my machine gun ammo to anti-personnel, check I've got a full tank for my devastating, immensely satisfying drill, and whisper a brief prayer to the gaming gods. There will be blood...

I lay down the Little Sister and wait. As she jabs her oversized needle into the corpse, a small progress bar slowly fills. Then I hear them coming: each demented shriek and crazed babble pounding at my heart. And then they come: basic Splicers at first, some bearing melee weapons - they're the ones that get gobbled up by the Rivet Traps - some firing weapons - they're killed by the turrets (hopefully). Then the Spider Splicers come, dropping from the ceiling right in front of me - my shotgun, which takes an age to reload, deals with them. It's frantic - I am turning and running and firing and using first aid kits in desperation, really. I am fighting to survive, fighting to protect my Little Sister. I am not hunting, I am being hunted. Then BioShock 2 pulls its finger out and rolls up its sleeve.

A Brute Splicer comes, BioShock 2's take on Left 4 Dead's tank. It is a muscle-bound freak, mutated beyond recognition. It throws anything it can at me, devastating my health with each hit. I try to use telekinesis to throw back, but it's not working. It charges from across the damp, crumbling corridors of Pauper's Drop - BioShock 2's fourth level - knocking me back, jamming me into a corner and, again, devastating my health. Nothing is working. I need to think - quick - or it's the Vita-Chamber for me.

And then it hits me: charge up the Winter Blast 2 plasmid, let fly with a block of ice, freezing him solid, then shatter him to pieces with a drill dash. The new dual wielding system makes it an easy technique to execute: I hold the left trigger, line up the reticule, then release. As the Brute is frozen in mid air, I hold the right trigger to rev the drill cannon, then press B (on the Xbox 360 - the version tested). I fly across the corridor and slam the drill into the ice block, shattering it in one devastating blow. The Big Daddy's drill dash is one of the meatiest, most satisfying video game attacks I've ever experienced.

Big Daddys are the least of your worries

I breathe, surveying my handiwork. Splicer corpses are everywhere. My turrets are destroyed and my Rivet Traps triggered. My heart is pounding. I loot, for cash, for ammo, for anything I can get my huge hands on. Then, I look for my Little Sister. Her creepy, glowing eyes stare up at me like a demonic cat. I pick her up and watch the ADAM count increase. I am fond of her. I worry about her. I need her.

Now, all I need to do is hold X to have a weird glowing white trail lead me to one of those vents the Little Sisters crawl around in, then decide whether to save or harvest my quarry. I am about to set off when I hear something awful. It is a shriek - a long, eardrum-bursting shriek - that shakes the screen. My Little Sister makes matters worse: "Mr B, I don't think she likes you playing with me..." A message pops up at the bottom of the screen: A Big Sister is coming and she is not happy. Prepare yourself!

The new dual wielding system feels as natural as you'd hope

What? Prepare myself? I've just consumed all of my first aid kits, Eve sprays and ammo fending off the bloody Splicers. Should I throw cash at her? Should I woo her with romantic Big Daddy moans and groans? There is no time to sulk. As the game has said, she is coming, and she's pissed.

A minute later, she arrives, leaping about and smacking me and teaching me a valuable lesson. I die, respawning at a Vita-Chamber. I frantically eke down her health bar; sporadic Electro Bolts into water pools buy me breathing space, two hits of Incinerate set her on fire, and thrown gas canisters explode in her face. Eventually, she goes down. My heart's beyond pounding at this point. I think I'm having a heart attack.

The first six hours of 2K's sequel confirm one thing: that it is a more combat heavy game than Ken Levine's 2007 game. The fetch quests, arrow following and slow, more disturbing, horror-focused moments remain, but they're juxtaposed by fighting that lasts longer. To get ADAM you need take down a rival Big Daddy and steal his Little Sister. Then you need to harvest two corpses. Then, maybe, you need to fend off a Big Sister attack. All three steps demand the player engages with intense combat. All three steps are risks you have to take. It is a relentless, tiring, exhausting process.

Thankfully, combat is, this time around, better, and more complex. Elemental affects now spread - the Rocket Spear ammo, for the Spear Gun, for example, fires a missile that lights anything it passes on fire before impaling enemies. Then it explodes. In one boss fight, I froze an enemy with Winter Blast 2 then landed a Rocket Spear into the ice block; the jet sent the block spiralling off like a balloon before exploding. Plasmids and weapons can be combined in more interesting ways; Splicers can be affected by multiple states. There's more going on; more chaos to cope with.

It's not quite "bigger, better and more badass", but clearly, since you're a powerful Big Daddy with more toys to play with, and not a spindly human being called Jack, you need to be challenged by powerful enemies; hence the Brute Splicers and the Big Sisters. But simply being a Big Daddy is not enough.

Some of the new Splicers are disgusting - the result of another decade of ADAM abuse.

If BioShock had a failing, it was that you could cope with everything it threw at you with the wrench, if you spent enough ADAM improving it. There was no need to play with Rapture's more elaborate toys because the most basic of them was good enough to get the job done. BioShock 2 forces you to play smart because it's a harder game. You need to lay traps, hack turrets and fire plasmid attacks into water and oil. But even that's not enough.

In BioShock 2 it is essential to research enemies using the new camera (which now records your death-dealing, rather than takes a snap shot). Research leads to bonuses, new abilities and, crucially, an edge over your adversaries. But to climb the research ladder, you need to kill in increasingly ingenious ways. This is BioShock 2's less than subtle way of forcing the player to sample Rapture's finer arts. Spamming everything with the drill dash is not an option.

Some fans have bemoaned this state of affairs. Some fans have bemoaned you playing as a Big Daddy (the original, in fact, a prototype called Subject Delta who is mysteriously awoken on New Year's Eve 1969) in the first place. Some fans have bemoaned the decision to set the game "Ten Years Later" (also the name of the opening level). Some fans have bemoaned the new villain, Dr. Lamb, claiming her rise to power as a socialist (in other words, an anti-Andrew Ryan) is a lazy, unfathomable cop out. There's quite a lot of bemoaning, isn't there?

She's a bitch, and she'll tear your heart out.

So, what do "some fans" want instead? A cursory glance at the Internet answers the question. They want to see the underwater paradise of Rapture fall to pieces for themselves; they want to see Andrew Ryan - perhaps the greatest video game villain of all time - in his pomp; they want to see Rapture's residents becoming the Splicers. Put simply, they want a prequel, not a sequel.

Are they right? It's impossible to tell at this stage. I've played the first five levels to completion, but I'm told I've barely scratched the surface (or should that be the bottom) of Rapture's terrifyingly beautiful innards. Certainly judgement will be reserved for the review, but, still, I'm confident in saying BioShock 2 will be a superb game. It's got all the atmosphere and dread of the first game, some great characters, and better combat. Dr. Lamb's voice taunts you as Ryan's did, making you question your every move (BioShock's legendary twist makes us naturally distrustful of everyone we meet). Lamb's daughter, Eleanor, and the Little Sister you're twinned with, occasionally fills your head with even more food for thought via sporadic flashbacks. There are loads of stunning set pieces. One sees you explore a children's museum in Ryan's Amusements, complete with animatronic scenes narrated by Ryan's disembodied, indoctrinating voice; at one point a giant hand appears, pulling a child from its parents as they sit, docile, in front of a television - it is as terrifying as it is impressive. Another sees you literally running for your life as you escape an entire level that's being flooded - eventually you make it outside Rapture's city walls, treading the sea floor and marvelling at the nutrient-rich water as Big Daddys were designed to.

Then there's Rapture itself. BioShock told its story not through bloated cutscenes but through messages scrawled on walls and audio tapes that told of the residents' descent into madness. BioShock 2's Rapture does the same - the little things combining to form one of the best-told stories you're likely to find this year. Pause for a moment in Siren Alley, Rapture's red light district, and you'll spy a male splicer picking up a female splicer. She wants a good time, and he's got the money to pay for it. It's impossible not to stop, look and listen to their astonishing conversation.

When you consider BioShock 2 has all of this AND genuinely game-changing moral choices, none of which I'll spoil here, a thought-provoking plot and a deeper role-playing system, it gets harder and harder to bemoan BioShock 2. We've not even touched on the multiplayer experience, either. So, the message is: stop moaning. You're better off preparing yourself for the terror that is to come. You'll live longer.

BioShock 2 is due out for PC, PS3 and Xbox 360 on February 9.