An exposition
So, in light of the BioShock movie being announced on the horizon, I got a little excited and decided to talk about what I think should and shouldn't be done to truly do it well. A list, if you will:
1) The opening scene. Nail this. The whole movie has to be strong of course, but as we learned from those first 20 minutes in the first game (there will be others, if you haven't heard), a strong opener is crucial.
2) The actors. Have some really freaking good actors that can do the insane screaming delusional thing like noone else. Presumably, there will be characters in this one with similar 'problems' like those in the original, so these need to be compelling and disturbing, which can only be conveyed well by great acting and hysteria. Have the actors for the Little Sisters be scary as hell, kind of The Shining-style, and not lame kid actors.

Also, personally I'd prefer a bunch of unknown or little known actors in this one, for some reason it seems only right. If I see freaking Ben Affleck playing the lead or something, I'll lose it (and nothing against Affleck).
3) The soundtrack. Nail this, too. Who knows when the movie will take place, but have the appropriate music to really fill out the atmosphere and add that extra depth to the game. If it's in a modern setting, perhaps still find a way to contrast 'happy' music with the atmosphere in the rest of the game, as before.
4) The first-person perspective.

This, I think, could be one of the hardest things to pull off. Either they'll have to find some way of transferring to a third person perspective and still have it be just as (or more) terrifying, or work with some pretty much unheard of method of shooting the entire thing (or most of it anyway) in first person. Either of these, if the director does it right, could be potentially amazing.
5) Direction. Don't direct it like freaking Pirates of the Caribbean or have any silly premises like The Ring (Gore Verbinski, who did these movies, is directing BioShock). Definitely, The Ring had some very frightening and dark moments, and that's what's keeping faith for me that this won't be a P.O.S. But if he just goes about it formulaically or inserts any cliches, the movie will suffer.
6) Special effects.

Especially for the plasmids, some amazing SFX will be imperative.
6) Story. Offer something integral to the series' storyline, hopefully something that couldn't be told quite as well as with a game. I expect this to be no problem though, as I assume 2K will be working with the writers. So, keep it rife with disturbing messages and ideals.
7) Atmosphere.

This is absolutely key. Basically a sum of all its parts, if you don't have the perfect atmosphere, it's pretty much useless. What'll be important here I think is to really capture that world underwater thing; especially on the big screen, and what with all them home theatre systems out there today, making a truly expansive and immersive world should be one of the high points of the film. One of the mild weaknesses of the game I felt was a lack of focus on the world outside the indoors. In the first scene (where you're first entering Rapture), I was blown away, but after that, we saw little of it, and what we did see wasn't mindblowing or anything. Which reminds me, get a blue whale in there. Oh, and on a related note, this needs to be in IMAX theatres.
This is just one fan's opinion anyway, but yes, a passionate one at that. What else do you think will be integral to the movie?