The game begins with no real introduction or backstory. You come-to underwater, in the middle of the ocean. Swimming to the surface, you find you have been in some sort of plane crash - the surface of the water is on fire, and luggage and debris floats around you. In the distance is a lighthouse-like structure floating in the middle of the ocean, inside which is an art-deco entrance to Rapture, a mini-submarine that takes you to the sea bed.
Bioshock is set in Rapture, an underwater city and failed utopia. Built by an ex-Soviet in 1946 for the world's cultural elite, it was to be a society where the best people can do their best work, unconstrained by government, religion and "bullshit notions of altruism". Rapture is a utopian, extravagant city, not made of steel and steam but wood and marble. Of course, this doesn't last for long. A stem-cell generating sea-slug dubbed 'Adam' is discovered, and with its abilities to alter the human form it quickly becomes a currency and valued commodity. This upsets the delicate balance of power and econonmy in the city, leading to conflict and power struggles with people using Adam to alter their biology for the more violent, physical struggle that ensues. You arrive in the early 60's to find the place ruined, much like SS2. Levine states "The focus is to create a world that we draw the player into as deeply as possible, even deeper than in System Shock 2".
As there was no conventional weaponry in Rapture, its inhabitants had to improvise and cobble them together with household items such as tomato tins, model airplane engines and office chairs. All weapons are modifiable, and Levine says "the weapons system alone is more complex and deeper than in any other FPS."
The most common enemy are the Aggressors - people who've had to mutate just to survive. Although they are now aggressive they are still aware of who they were and what they have become. Any enemy can use any weapon found in the game, and can have abilities such as climbing walls and ceilings.
Gatherers are children who obtain Adam by recycling it from dead bodies. They are protected by massive mutated pet-like beasts, Protectors. These go about their business in Rapture, and wont bother you unless you bother them. It is possible to befriend Gatherers and share some of their Adam, but the only way to get all of the valuable Adam is take on their tough Protector and actually kill the child. Levine says he intends this to add to the real moral choices within the game. As the game progresses you get to learn the story of the Gatherers and how they have been exploited.
The skill system is similar to SS2, with abilities, 'plasmids', purchasable using Adam at plasmid stations around Rapture. Once these abilities are installed, they cannot be changed until you reach another plasmid station. Abilities can affect strength, agility, etc., or even the AI, turning Aggressors to your side and fighting other enemies.
The AI is important, says Levine. It is intended to be a world where there's an active ecology, each character and enemy having their own motivations and behaviours, and interacting with each other and the player. The player will be able to interact with and impact this ecology, affecting it in planned and unplanned ways. Unlike SS2, the world and areas are open-ended, and the gameplay much more emergent.
Using a 'heavily modified' Unreal Engine 3, the screenshots look very promising. Huge creatures, variously clad in old-fashioned divesuits and mechanical apparatus, tower menacingly above the player. A tiny, shoeless Gatherer in a pink dress is seen running away through a garden-like area covered in foliage. The intact city is elegant art-deco, clad in wood with exposed metalwork and detailed furnishings. Streets are lined with bright, retro-styled neon signage. In SS2 style, 'Gene Traitor' has been scrawled in blood on the wall of an extravagant bathroom, now flooded.