As if anything I've said so far isn't an indication, readers will be subject to multiple and explicit spoilers regarding the plot to Bioshock Infinite and should hesitate before reading on if they wish to avoid this information.
Let's start at the beginning of the game with Booker being ferried to Columbia courtesy of Rosalind and Robert Lutece - who, like most of the main cast, are of course the same person across different universes. We know from the ending that Lutece brings Booker through a tear to this world and charges him with rescuing Elizabeth, but under what motivation? We also know that Lutece is responsible for Elizabeth even being in Comstock's universe but she/they have no personal responsibility to her nor anything to gain from the success of Booker's mission. One could argue that they feel sufficiently guilty for being party to Elizabeth's imprisonment and misery but this argument is moot when they have access to a machine that enables them to go anywhere at any time. They could have simply rescued the infant Elizabeth and returned her to Booker, thus ending Comstock's plan for a successor and removing any need for the events of the game to take place.
They are also shown as being psychologically detached due to their personal knowledge of the truth about multiple worlds and parallel universes. They repeatedly state that past, present and future are the same and that every possibility occurs simultaneously across infinity. If this is true then why would they aid or interact with Booker at all? It would have been a much neater and more poignant hook to the game if Elizabeth herself unwittingly drew Booker into Columbia's universe. At a couple of points in the game she explains the process of opening tears as a form of "wish fulfillment". Her desire to be freed from the tower would draw to her the one man - the one Booker out of all "Bookers" across existence - who could achieve it. In doing so, Booker loses his memory just as he does when brought through by Lutece. He maintains the self-delusion of "save the girl, wipe away the debt" and heads to Columbia to act on his impulse. Lutece could still be incorporated into the game in almost exactly the same capacity: observing Booker and recording his "constants and variables" as if he were a rat running a maze. Evidence in the game including the important coin flip scene show them doing just that anyway and that in at least 122 other universes, there is a Booker DeWitt carrying out the same task. The explanation for Booker's arrival given by the game is clumsy and makes no sense if you accept everything else that transpires.
Now onto the central issue and addressing the very final moments of the game. Booker sacrifices himself in order to erase Comstock - his alternate identity in a parallel universe - from existence, thus "saving" Elizabeth by preventing every event of her life from happening altogether. I understand why the writers went down this route as it provides an emotional climax and demonstrates Booker's resolve in addition to drawing everything to a close. But the problem is, it doesn't do the latter; at least, not if everything else we have been told is true. We know that the main Booker - that is to say, the player's character - never actually becomes Comstock. He rejected the baptism in the creek and therefore was never reborn to create Columbia. It is a parallel Booker who accepts baptism, becomes Comstock and subsequently enters a tear in order to acquire Anna whom he raises as Elizabeth. Therefore, Booker's death changes nothing on two counts: firstly because Comstock's spiritual conception has already occurred and secondly because it occurred in another universe to another man.
One theory suggests that the creek acts as a nexus between the universes and Elizabeth has become powerful enough to allow the one death to resonate out across the continuum. But if the context of the post-credits scene is to be believed, there is at least one more Booker who perdures and that he never surrendered Anna. This theory is backed up by the fact that following Booker's drowning, all the parallel Elizabeths present vanish from existence save for one. Hence it feels like a moment of forcing the narrative when the player's Booker has to die in order to destroy Comstock.
It also bothered me on a much more personal level that during the ending, Booker and Elizabeth never went to Paris. It was such an established theme of the game that the two never simply spoke of "escape" or simply "let's get the hell out of here"; rather it was always about "I can't wait to reach Paris". It would have made sense for Elizabeth to open a tear and take them there so she could see it just once. It's implied that once she regains her powers she already realises the truth about Comstock's identity and understands what will transpire, hence why she questions Booker's decision to "smother the son of a bitch in his crib".
If I had written it, my ending would have been very different. Elizabeth would have taken the pair to a universal nexus but instead of being a country creek, it would be the Battle of Wounded Knee as a Native American village burns to the ground. Here, the player would fight the final boss: Booker DeWitt. The same Booker DeWitt who would become Comstock in the future of that timeline. He would be a dangerous, cowardly man: one who would accept orders to butcher innocents and then find false hope in religion in an attempt to save his soul. In this battle, Elizabeth could still open tears to Columbia, bringing through weapons and supplies, but enemies might also be pulled through, adding multiple threats to deal with.
With DeWitt's death, the presence of Comstock would be erased from the timeline, leaving the reality that we see in the epilogue in which Robert Lutece never came to Booker and Anna is still in her room. Meanwhile, Booker and Elizabeth are seen on top of the Eiffel Tower, standing in silence. As the camera pulls away, the millions of lights in the city become stars, echoing the image previously seen when Elizabeth refers to the stars in the sky as each one a door to another universe. The game fades to black and the credits roll.
But what do I know? I'm only one man.
