Hahaha I just felt the ending was sort of contrived in a rush. I mean it makes no sense when you really think about it, people defended it by saying that critics don't understand it but most critics actually do and that's why they have a problem with it. I mean first off, drowning future Booker wouldn't have the same effect as drowning Booker earlier in the timeline so it makes no sense that the Elizabeths would all be gathered to drown him, but even if we rationalize that, it just creates a grandfather paradox, whereby their actions cancel out their ability to commit their actions and thus either break the space time continuum worse than dividing by Zero, or cancel out their actions or create a time loop.
Then it gets even worse when considering that there are supposedly infinite universes for every potentiality in the BioShock universe now, all drowning Booker would have done if we accept everything up until this point is cut off one particular branch of an infinitely expanding tree, and similar events and worse would still play out on other branches.
And even if we get past all of this, it's profoundly selfish and arrogant for Elizabeth to eradicate entire universes just to avoid living through the problems with her own particular reality. The only way it would even be understandable is if by the very nature of her reality one branch would eventually destroy all the others, making it a lesser evil sacrifice, but that potential narrative was never explored in the story line.
Ultimately what we got was just rushed made up on the spot Bull Shit it seems.