The precedent to which all future first person shooter games should strive to emulate.
Such was the genius (or madness?) of Andrew Ryan, the founder of Rapture, built as a sanctuary city far removed from the oppressive shackles of society, and away from the tyranny of kings or the ever present eye of government. Before entering the city proper you are met with a huge banner reading: "No gods or kings. Only Man." This simple statement really sets the tone that Andrew Ryan envisioned for Rapture; there is no such thing as faith to cling to only the hard work and sweat from your brow. It is perhaps this ideology that played a pivotal role in its downfall.
When you first step foot in to Rapture it may appear to be deserted, but as you quickly discover you are not alone. As you emerge from the underwater submersible that carried you to the city from the surface, you discover that the city of Rapture is still very much alive. Roaming amid its leaking corridors and disheveled rooms are splicers, big daddies and little sisters all in search of one thing: Adam.
Adam is very important, and it is the major resource in Rapture. It is the currency with which you use to buy "plasmids." Plasmids come in two types: Elemental (fire, etc.) and physical (telekinesis, etc.). With these elemental/physical powers in collusion with more conventional weapons such as a shotgun, machine gun, pistol, etc. you undertake the task of fighting your way through Rapture and its deranged denizens to find out the truth about this enigmatic city and yourself.
Splicers are addicted to Adam and they won't think twice to kill to get it. Little Sisters go around collecting Adam from dead bodies and big daddies accompany them as their guardians against the splicers. Splicers are really nasty buggers as their craze for Adam has driven them insane. They come in a variety of types; some will charge at you with a pipe while others wield guns and plasmids just like yourself. Some even crawl on the ceiling and attack from above. Whatever the variety they are pretty easy to kill with a combo of plasmids and firepower, but don't underestimate them as they can be pretty crafty in their strategies.
The tougher nuts to crack are the big daddies and you will have to fight them in each level. Vastly different from splicers, these guys require some serious planning, preparation and firepower. You need to kill the big daddies in order to get to his little sister which is where you get Adam in the game. Now once you have the little sister in your grasp you can either choose to rescue or harvest her. The former grants you less Adam but the little sister lives. If you harvest her you get the maximum amount of Adam but you kill the little sister in the process. Decisions, decisions….
Along the way you will meet a host of characters that seem to appear to want to help you and some that wish you extensive harm. All of it leading up to a climatic confrontation with Andrew Ryan himself. It is at this point that you discover a rather shocking (no pun intended) revelation which brings all of your actions up to this point in serious consideration and which, if you have been absorbed in the narrative, turns the game on its proverbial head. It's that big! From that point on you undertake a very different mission as you learn the dirty little secrets Rapture has been keeping.
BioShock proved that first person shooters don't all have to be about mindless shooting with lackluster, skimpy storylines. 2K Games did an outstanding job because they combined sharp game play with challenging levels, smart writing and artistic vision that all future first person shooter games should strive to emulate.