Seriously, why would you change anything about the story of Bioshock 1 if you make the movie? You have huge plane crash, maybe even some weird, unexplainable flashbacks, in the beginning as the guy is coming up for air. There's your big bang beginning that Hollywood whacks off to. Leave the main character a mysterious man in the beginning and set the movie in the late 60s or early 70s. Hell, you could even set it in the current time if you really wanted to, it wouldn't lose any effect (personally, I wouldn't go past the late 80s; Ryan and Fontaine can't be 90 year-old men but they could lessen their age state pretty easily using plasmids). Swimming to an island shore he stumbles upon the partially hidden and obviously abandoned entrance to Rapture. Having nowhere to go and being off in the middle of nowhere, he stumbles inside looking for a way to contact people for help.
What does he come across? This barnacle-filled relic of the late 1950s, almost like a time capsule with a grand hallway making reference to Andrew Ryan and the utopia of Rapture. Man stumbles upon a working elevator and takes it down into the world of Rapture. On the way down he gets a great little greeting straight out of the 40s welcoming you to this new underwater utopia and what it means.....except everything seems deserted and generally undermaintained for the last 20 years, including some leaks in place that have obviously been feeding the barnacle buildup. From there, he slowly uncovers the mystery of Rapture, Andrew Ryan, his opposition in Fontaine, and even comes across a few of the audio diaries of long-dead citizens which he plays along the way to deepen the world.
And if they did it Dark City-style (by far the best way to shoot it, IMO), you could even introduce some form of the plasmids and maybe even work in the Big Daddies and Little Sisters, although that may be a little TOO fantastical for a film. You may have to leave that element out but having the people be all hopped up on plasmids is actually a pretty neat premise for a zombie-like film, but with a far deeper storyline.
Really, in Bioshock's case, there's very little adaptation required beyond what's already there. It's the one games film that would work very well almost as is.
I was there on that fateful day, were you?