And this article is going to involve a lot of spoilers, so you shouldn't read it unless you've already beaten the game.
Anyway, I wanted to take a look back on the series in retrospect. Bioshock was a successor to System Shock, which sadly I haven't gotten around to playing. Bioshock 2 was awful: it suffered by trying to follow too much in the first game's footsteps. Infinite solved this by re-imagining the series with a completely new setting and tone. But it's the ending of Infinite which ties it all together, with its revelation of the interconnectedness of the settings. Infinite wisely stepped away from relying too closely on its predecessor, but then it faked us all out and returned to its roots in the best possible way.
The ending leaves open a lot of possibilities for future installments. By revealing a repeatable template (there's always a city, there's always a lighthouse), they open up the way for future creations centered around this template. What irritated me, however, was that they refused to give us any hints. I'm not expecting them to have a whole new game already planned out, only the slightest hint of a theme, another example of the template to go off of (or even to lead us astray). The only two templates shown in the ending are in fact the two existing ones, the lighthouses outside Rapture and Columbia. Why not show us other examples of lighthouses as well, for potential future city themes?
Then there's the final ending revealed after the credits, in which we see through the eyes of a (now alive) Booker DeWitt. The DeWitts killed in the ending were only those which had to die to prevent the future Comstock from happening. This means that the player can now only follow potential DeWitts unrelated to the events of Columbia and the Comstock personality. Curiously, since this has been totally withdrawn from the timeline, the timeline has reset: in following the typical theme of mistakes in space time which seek to correct themselves, Elizabeth has in preventing herself from being slave to Comstock also prevented herself from ever gaining her special abilities in the first place. The event has been completely severed and the timeline reset. Now we follow a DeWitt who lives a (relatively) ordinary life in which Anna is never taken from him and he must raise her on his own.
Where does the downloadable content, which is supposed to continue the story, continue, then? Perhaps expanding an earlier point before the severing of the timeline, or perhaps the universe double-course-corrects itself and forces DeWitt to return to Columbia even in this timeline. What would it be without him, without Comstock? I imagine that the new content may in the same sense reimagine the old content, replaying through familiar levels but with a radically altered setting and ideological tone. This would be a Columbia which had developed along completely different lines, similar to the way that Bioshock 2 explored ideological themes contradictory to those of the original. Or DeWitt could never return at all, and perhaps the story might be told through the perspective of another character, or Booker may go through another trial altogether. Hopefully however, more care will be put into Infinite 2 (for lack of a better title) and it will be a good game in its own right, rather than trying to lean too heavily on its predecessor.
Ideological exploration is what separates the Bioshock series from the common shooter, and what marks it as a rare breed in the big budget game crowd. Other games have tried, and often failed, to actively explore important themes during gameplay the way that Bioshock has, but few have done it so well. When you get things like Metroid trying to explore really sexist themes of “motherhood”, it's hard to imagine that Bioshock could come out of a closely related market. Bioshock is good at exploring these themes partly because it likes to be critical, and never blindly endorses anything. In willing to take a critical jab at many different ideologies (capitalism, socialism, racism, religious fundamentalism, anarchism, minority politics), Bioshock brings a certain wisdom to the table in the vein of the new post-modern age of Zizekian anti-ideology. The cities of Bioshock are, as it were, the negative in which Zizek advises us to tarry, in portraying for us a picture of ideology at its worst and most brutal. The city is the hole through which we can see ideology as it is, in all of its glory and all of its shame.
I'd be interested to see Bioshock take on some other interesting ideologies of today, including democracy, fascism (this one seems like a no-brainer, since it's the dominant one in many shooting games, particularly WWII shooters) feminism, and queer politics, to name a few. Cities in volcanoes, floating on the ocean, on space stations (I feel like this is what System Shock did, right?), future cities, cities of antiquity, all of these are also options. The combinations aren't endless, but should provide enough interesting material for future installments, if they intend to continue with the series in a similar format.
Another interesting point is the feminist-friendly nature of the series. Female characters are just as common as male characters in the series, and the bad guys are often bad gals. The little sisters were perhaps not very gender progressive, as the primary female characters of the first game they spend their entire time being guarded by protective male 'daddy' figures. However, the relationship more closely mirrors that of a brother/sister relationship, given the innocence of the little sisters, and the brother sister relationship being often more primal than the child/parent relationship or the adult male to female relationship, it is a more innocent relationship, untainted by cultural norms. While men in the series are often in a position of power, and the plot centers around male actions, the female characters generally manage to hold their own, often being doctors or other respectable supporting characters. Bioshock 2 inverts the male dominance of the first game with a female dominance. The endings in Bioshock 2 and Infinite place a great stress on female characters and Elizabeth certainly comes into a position of great power at the end of Infinite. I was refreshingly pleased by the nature of Elizabeth and Booker's relationship in Infinite; it proved that two white, attractive protagonists don't have to hook up. Of course, this is later revealed to be because he's actually her father, but this doesn't diminish its power in the slightest.
The gameplay of Infinite centers around one massive escort quest, yet it also decides not to make Elizabeth useless. Other games which heavily focus on escorts generally make your female companion weak and useless, ala Resident Evil 4, Ico, etc. Often these characters are 'redeemed' by the fact that sooner or later they prove to have one minor and mostly useless skill that happens to be the only thing that can get you through a highly contrived puzzle, as if this was enough to make up for the fact that otherwise they just run directly into danger while being made of something weaker than paper. Elizabeth, however, is a highly useful ally in her own right (see above): she summons weaponry and tactical advantages, gathers ammo and health for you, and just in general acts as useful as she can. As an added touch, she lingers in the world around you, looking around excitedly at all the sights, a hilarious contrast to the usual player's policy of rushing through areas, desensitized to the environment by the fast-paced nature of gameplay. She doesn't take damage or require saving, and in most cases saves your life in sticky situations. Her ability to pick locks is not her single useful skill, but rather just another skill in a whole lineup of ways that she's useful to you. In short, Elizabeth is often more useful than you are: it's no wonder that you're the one that had to go, in the end.
While Bioshock has never been outright feminist (and I mentioned above that this would be a great topic to tackle in future games), I have great hope for its ability to touch on those themes. But then, only time will tell. Only the future can tell us where the Bioshock plot will go next.