Infinite's ending was incredible.
Among all of the craziness that was Infinite's story, the whole idea of Baptism creating a different person, and being a recurring motif, was mind-blowing to say the least. That this simple event of washing away your past (to find solace or forgiveness) could change so much. And being that it is used multiple times throughout the game, from drowning Comstock, to Songbird drowning, to drowning Booker at the end, was incredible as well.
I have not seen this kind of brilliant story-writing since 999/Virtue's Last Reward.
Especially considering Infinite's ending is very similar to Virtue's Last Reward, dealing with the same Multiple Worlds Theory
I cannot say enough good things about this game. (or all three of them, rather)