Okay, I'm sifting my way through the posts here and thought I'd just touch upon a few things I haven't found fulfilling answers to. If somebody else already offered up an answer to them, please let me know and I'm sorry I missed it. Here we go:
1. I don't get how or why Elizabeth can open tears. It's simply never explained. Do the Luteces "infuse" the ability to her after bringing her to Columbia? That's the only answer that seems to fit with the rest of the story. Why do they give her the ability to open tears at will though?
2. When Elizabeth(s) kill Booker by drowning/smothering him, aren't they actually killing the Booker who already made his choice not to be reborn? As far as I understand BS: Infinite's reality-jumping mechanic to work, when you step through a tear into another reality, you DON'T replace the "you" in that new reality; you're simply a "copy," if you will (albeit who made different choices, etc.). This explains how "Booker" is able to come to Columbia and NOT BE "Comstock." They're separate people. So why when Booker steps through the tear to the moment where he chooses to be/not be baptized, how does killing THAT BOOKER stop the decision? He's not the Booker of that "universe!"
3. I'm unsure if anyone has explained what the outcomes of the choices you make in the game are. i.e., what happens when you choose heads vs. tails? What happens when you choose the bird necklace instead of the cage necklace?
4. Who is the Archangel? I do not have a satisfactory explanation for this. It COULD be a number of people. It could be Elizabeth from the future, manipulating Comstock in the past. It could be there is no Archangel, just Comstock peering through tears. It could be Lutece, but that makes no sense either. Many of Comstock's actions are taken because an Archangel is telling him what will/won't happen, but we never realize who that Archangel is.
5. How the fuck old is Booker supposed to be?! Since the baptism is the inflection point in the branching timelines, we have to figure out how old he is during that moment. Wounded Knee took place in 1890 - 22 years before the majority of Infinite "takes place." We could guess makes Booker about 20 when he is baptized, which would put him at age 42 by the "time" he goes to Columbia. You never get a really great look at Booker during the game, but he sure doesn't seem to be in his 40s.
The reason I put "takes place" and "time" in quotations is that when you're in Columbia, it's not 1912 at all. In fact none of the game really takes place in 1912 - only some of Booker's memories do. The universe/timeline in which Booker goes to Columbia to rescue Elizabeth must take place sometime in the 30s or 40s, because Comstock is definitely in his 60s or 70s. I guess time is kind of irrelevant in Colubmia considering that it's floating in the sky and cut off from the world. Oh, and also because reality-bending tears have been exploited to bring technology through from other times/worlds.
6. Somebody needs to make an infographic so we can keep timelines/alternate universes straight. That somebody might end up being me.