Andy: I might be able to reconcile it if it was a revelation we had more time to digest, but getting it in the last sentence of the game speaks more of "Behold my twist ending and despair!" than of any truly necessary character development. There are some signs earlier in the game once you know to look for them, but nothing that really indicates how we got from moderately remorseful dog of capitalism to greedy, spiteful, omnicidal maniac, which is a problem. You can speculate about alternate reality Bookers and/or being led to a particular outcome via the method intended for Elizabeth that's described on that one voxophone, but I find this much too large a jump to be left to assumptions. Also, I just cannot make the chronology work in my head. Did Booker/Comstock really take just two years to go from relative nobody to having enough charisma and clout to build a floating city and populate it with a mass of zealous followers? Or did he start smaller and then go back in time to do it again more professionally and on a grander scale later and that's why Comstock looks so much older than Booker, so things just got worse and worse through repeated cycles? If hanging around Elizabeth for a couple years was what left him sterile, then why did he need to go back in time to get someone of his own bloodline in the first place?
You can approximate answers for much of this stuff, but it bugs me just because none of it feels necessary. Explicable character development needs to trump crazy plot twists. Admittedly I missed something like twenty voxophones, which annoys me greatly.
Other stuff that's belatedly occurred to me to mention now that I'm not frazzled from shooting dudes for six hours straight:
-It amuses me how casually they handwaved the whole "How does it fly?" question. Quantum mechanics? Good enough for me! Also quantum uncertainty as an explanation for ghosts, as good an explanation as any. Anytime there was an NPC around unsure of its vital status was some quality creepiness.
-Discussions about the grammatical implications of time travel? Aw yeah. You know, I can't help but wonder if Rosalind Lutece's brother is really just another her pulled from a reality where she happened to be male. He did just kind of turn up out of nowhere one day, as far as the public knows!
-Is it just me, or is enhanced Bucking Bronco + shotgun a totally broken combo? Any mob without heavy hitters can be completely neutralized that way.
-Last minute addition for Grefterpost: I came away with the impression that the Elizabeth horde genuinely drowned him at the end.