In an underwater world, where FPS meets RPG meets Survival Horror, only great things can happen.
This game is incredible 99% of the time. The story, though at times it may be hard to follow, is very impressive and complex and should help keep you playing for a while...and of course, complementing the story is only the gameplay. The plasmids and tonics increase the fun you will have. Such as lighting an enemy on fire with Incinerate, and just as he dives into a pool of water, you use Electo-Bolt on the water, electrocuting your enemy. Or hacking an enemy camera so when another enemy, such as a Splicer walks by, the camera sends bots to attack him.
Then there are the U-Invent station where you can create useful items and the Power To The People stations where you can give your weapons upgrades, in case Plasmids aren't your style. Don't like the pistol? Quadruple the clip size! Don't like the shotgun? Cut the reload time and give the bullets a damage increase! The sounds are incredible, hearing the insane Splicers, the giant Big Daddies, and the Little Sister 'harvesting Adam from a body' are just a few of the ambient sounds of Rapture.
And the incredible, dark art style, picture Gears Of War's decay art style, but better and underwater. The graphics in this game are almost second to few. Trust me, you'll stare at the water at least once and say 'Wow....that's cool'.
There are some glitches, such as dead bodies moving and the like, but that rarely takes away from the game experience.
Buy Bioshock, no, seriously, run!