A few random thoughts, my theories are not too cohesive this season, as I find things are changing too fast to really make these kind of broad "what's this show about" predictions.
One thought is that while I've believed the general idea that it was never jacob in the cabin, and that Christian was really the MIB... Christian appears off island, and I don't see how that makes sense for MIB. Thus I'm realizing I know nothing of the MIBs cabal, his side, what role they play and who they are, and how generally supernatural they are (the dead risen, an able to appear all over the world).
Anothing that struck me watching the latest episode is how trashed all the characters have been by any fiction standards except perhaps cynical novels. Watching Claire is depressing... she's insane and wasted, to the "animal skull as proxy for baby" level of crazy and that's some serious crazy. I liked the idea of the island as purgatory and even while that was never going to be literal, it continued to seem metaphorical in the first couple episodes where we saw everyone had their skeletons in their closets, and seemed to work them through on the island.
This went well with Rose's experiences being physically cured, and that the island has this power and takes healing action based on a person's wellness. But then it swerved away from that rather harshly... sure, the people that leave have a terrible time, but it stops looking like this is due to the island healing them, and just literally because the island wants or needs them for something, whether it's good for them or not.
Indeed, the show never asks "is this good for you" it only asks "is it good for the island"... the island punished them for leaving, rather than leaving them to their own devices which fail. There is still some growth, like Sun and Jin being in love, but Sun also has grown much scarier. Jack is in a good place mentally, but broken down over all, essentially lost, seeking by wandering, playing russian roulette with dynamite.
It's rare a show will do this to it's characters, and really to all of them. I think the only one not being subjected to this is Hurley, so maybe he's the one in the end. OTOH, it could just be so they don't ruin him for comic contributions. (Hurly starts torturing people?)
I wonder in the end if there will be any redemption for these characters.
-Sympathy for the Devil-
It's clear that Lost likes to be ambiguous about good and bad, and all bad guys say they are the good guys. But we really tend to keep believing one of these is good and one bad, even if it's ambiguous, even if the good side has done some bad things... it's still the good side. Like us all, I'm prone to this, even though I would love if the point is that both sides were bad.
Still, I have thought that yes, Jacob represents the good, I mean, MIB has crazy people on his side, and kills a lot. But then, seems to me Jacob has plenty of blood on his hands one way or another too, and we don't know the situation... a powerful creature caged can in fact be expect to fight back for its freedom.
I don't know if it's something about the way he's acting, and unintentional, but the Jacob character comes across worse to me than MIB-locke. MIB-locke seems a little more honest, a little more human and humble. The way he reacted to Claire attacking Kate, for example, seemed out of character for a monster that just likes to kill. While he's murderous, it implies he's not merely blood thirsty, and is not using everyone merely as pawns, possibly. He seemed to truly promise protection. Jacob's character is much more manipulative... it could just be the mystery of power... moving in mysterious ways, but I don't respond well to that idea of mystery, so Jacob seems to me simply manipulative. And the tone of voice and expression when he tells Hurly at the lighthouse that "bad people" are going to the temple seems very sanctimonious... while still he doesn't give real information, just enough to get people to do what he wants.
End of brain dump.