I have completed this game so I can confirm the story it absolutely top notch.
Really never expected such a big twist, I never expected the game to be so detailed and perfectly executed it is indeed one of a kind and for shoot em ups to have a good story along with them is extremely rare in most cases but Bioshock should make the employees of 2K very proud.
Each level brings along a new unique character and plot to deal with some may seem pretty damn boring but when you get to the cinema type place that is indeed fantastic, some parts are so sick and corrupt its pretty hard to even imagine thinking of this kind of scene in the game so the designers must have thought long and hard how to make each level unique compared to the other.
Don't get me started on the Plasmids or Weapons because they're simply brilliant, even the hacking is kind of fun simply because later on you need to be pretty fast to get all the items in place to crack the safe/door/security.