What I like about the initial setup of story is the Greek tragedy kinda thing, that there was absolutely no good choice to be made; that whatever Sam did, he had been damned to lose his brother.

Now, the disintegration of Sam is just fascinating and horrible to watch, because he's remaking himself as much as Dean, if not more. He needs to be the older brother, the mentor, the physical one, the responsible one. The abomination. The haunted. The fallen. The one who did the saving and got damned for it. Taking any shard of happiness he can get and making his life around it. And he's spiralling so far from Sammy-then and into the fairy land of lies that at some point there may not be anything left.

Well, at least that's what my busy little reader's brain sees for now. I'm very curious what the conclusion will be.