Bioshock is a game about choices: making them, regretting them, punching the air when they go spectacularly well and occasionally finding out you haven't made the right ones at the right time. It forces you to make tough decisions, tempts you with dozens of different powers and weapons, and makes you feel the consequences of your actions.
Sure, at heart, the game's mostly on rails, using the linear ghost-train approach to shocks and plot twists pioneered by Half-Life - but that's no bad thing, because Bioshock learns, and improves on what's come before. The opening, where you take a guided tour through the city of Rapture in a bathysphere, is a flawless aquatic homage to Valve's classic.
The various bits where you pick up a weapon only for all the lights to go out are textbook Doom design, but the addition of giggling voices in the darkness makes them much, much scarier. The option to reveal chunks of plot via audio diaries mimics the developers' earlier System Shock games - which used emails - but because you can listen, rather than read them, you're much more likely to take in what's going on. Set-pieces routinely unfold while you're on the safe side of a pane of shatter-proof glass, but you're also constantly getting a sense of what's going on from your surroundings - from subtle architectural details, ambient noise, discarded items, and adverts. The city of Rapture tells a tale of its own - far from being a stale collection of corridors and rooms, it's a recently-deceased paradise where every area has its own personality.
The art deco designs, retro adverts and ever-present 50's music give it the feel of a place that might have been fun before people started getting sliced up and shoved in cupboards. The constant references to founder Andrew Ryan paint a stark picture of a man driven mad by his dreams. If it didn't do anything else, Bioshock would be worthy of awards for its services to storytelling alone.
But it does a lot more - although you're subtly steered through the game's events, how you survive them is completely up to you. And this is where the choice comes in: you fight the game's enemies, known as Splicers, with a combination of traditional firepower and genetic upgrades called plasmids. The trouble is that you're painfully short on both: one blast of the electric shock ability will merely stun the enemies and three blasts will completely drain your energy. Finding an entire clip of machine gun ammo is pretty much cause for you to start partying - you're far more likely to find a couple of bullets by looting disfigured corpses and rummaging in lockers. This forces you to get a bit creative.
Use your Incinerate power on an oil slick, for instance, and it'll go up in flames, setting any nearby enemies on fire. Because they've still got dregs of human intelligence, the Splicers'll run for nearby water - but if you've got the Electrobolt plasmid, you can deliver a lethal shock when they take the plunge. Everything and everyone reacts as you'd expect it to, both physics-wise and psychologically so. This means that it's always possible to discover new combinations, making for some beautifully intuitive gameplay. What's more, you've always got two, but more likely three or four, ways of tackling any given situation thanks to multiple ammo types and the huge variety of options on offer. Security turret giving you grief? Hack it so that it ignores you and shoots your enemies. Rubbish at hacking?
Upgrade your abilities with a tonic, or freeze the unit with the chemical thrower gun or Winter Blast ability to slow down, and therefore make the process easier. Still rubbish? Spend some of your hard-earned money to bypass all that hacking nonsense, trusting that you won't need the cash for bullets when the turret mows down all your enemies. Can't be bothered with any of that? Just blow the turret up, but be aware that you're getting rid of a potential asset against the Splicers.