Now as the plot is a really important part of the game; I'm not going to give that much away. What I will say is that you play a man called Jack, and at the beginning of the game your plane crashes into the sea. You escape the wreckage and go into a lighthouse where you find a 'Bathysphere'. You step in, pull the lever and are lowered towards Rapture.
Rapture is an underwater city, the brainchild of the brilliant Andrew Ryan. It was supposed to be an enlightened city, where the arts, sciences and other noble pursuits could be advanced without the limitations of society. Without giving too much away, it all goes to pot and you pretty much see the society fallen apart and before too long are fighting for your life, both with guns and with plasmids.
One of the main creations of the game is the plasmid. The inhabitants of Rapture inject themselves with a drug called Adam, which grants them a variety of powers such as telekinesis and the ability to throw fire, freeze enemies and even throw lightning. Using these abilities takes up EVE, another chemical you have to inject yourself with, which functions as ammo for the plasmids. Now, they aren't just used as weapons, that would be far too normal for Bioshock, they are also used for a variety of puzzles and also to access other items.
Resource management is a big deal in Bioshock; do you spend money to get items from a vending machine or do you use up some EVE to melt some ice and get the items that way? As well as the plasmids you have normal guns that can be upgraded and that require ammo, so it's often a choice between spending money to get EVE or ammo, spending EVE to get ammo or money or any other combination. There's a lot to think about!
There is a fair amount of enemies in Bioshock but they basically boil down to two main types. There are the various types of Splicers; normal residents of Rapture who have gone crazy and who kill for Adam, and they come in various forms and weapon sets. Then there are the Big Daddies, massive formidable foes in diving suits who guard the gatherers; mutated children who extract Adam from dead bodies. Now the game poses you a moral question...
After killing the Big Daddy you have a choice of what to do with the gatherer they were protecting. You can either rescue them; returning them back to normal children, or you can harvest them, which means killing them and getting Adam straight away. The benefit to rescuing them is after every three or four rescued you get more Adam than you would for harvesting them, as well as some extra goodies like specialist tonics (a passive perk) and of course a sense of well being for not murdering a child.
You'll hack quite a lot throughout Bioshock. When turrets and sentry bots (shown in the picture above) are hacked they will stop shooting at you and instead gun down your enemies. Another helpful thing you'll hack are Security cameras which when hacked will send out sentry bots against your enemies, which is marvelous for Big Daddy fights.
The hacking itself is like playing a mini-game of Pipe Dream (which if you missed, requires you to put the correct pipe sections onto a grid so the water doesn't pour onto the floor). This is an interesting little mini-game but after a while you'll usually end up paying or using an auto-hack perk to avoid it, making the game a little redundant but nice while it lasts.
The whole of Rapture has an art-deco style, and the consistency of the decor and the score give the world a unique and almost nostalgic feel. However, knowing that madness and psychopaths run rampant throughout the city keeps you constantly on edge. This creates an interesting juxtaposition of the beautiful, albeit abandoned, city which contrasts with the bodies and blood, giving a level of immersion that isn't readily duplicated. The only other game I think comes close is Dead Space.
Along with the look and the score of Rapture, the sounds of the survivors truly bring it to another level. On your journey throughout the game you'll find women weeping over the corpses of loved ones, audio journals talking about the fall of their civilisation and the madness that followed, and ever present bodies and grusome tableaux that keep you on the edge of your seat, wondering what twists and turns await through the next door.
So basically, Bioshock is awesome. I personally haven't quite finished with it as I've still got to play it thorough on hard without dying once, it's hard difficulty setting is actually hard, unlike most games these days. The huge variety of plasmids and weapons and the customisation that you can go through will allow a variety of playthroughs to try the different ways of getting through the game, and as I've said above, the atmosphere and immersion in Bioshock is simply stunning. This is a game you have to play.