The NonMother's Death
I got the distinct impression when she said "thank you", that to get out of the role of guardian, you have to find someone to betray (and kill) you, and someone to take your place. Like Ben to Jacob.
Who is good
So while I would have liked jacob to get blasted with EMF to become the guardian, and the light to have been some quantum mechanical field instead of life and goodness... fact is those can still be metaphors for what it really is. Maybe she had a primitive view of it.
And on the narrative side, I liked what Across The Sea said. The good and evil were not purified. MiB's motivation turns out to have been justified. His mother was crazy, and if there is some metaphysical reason, like her purpose being true and vital... she's still like a vengeful goddess and no good to deal with, a maniacal murderer of no remorse. He killed not his mother, but the woman that killed his mother.
I also LOVE the motif that the bad kid might do the right thing. Given a crazy mother, the "good kid" is more likely to stay with crazy mother. And also, I win, I had always wondered if Jacob's sanctimony was just the way he acted or if it was directed. But it was the mother's sanctimony, a muderous sanctimony. And I think Jacob's cold bloodedness is confirmed now, however guilty he may be, or whatever his practice over centuries...
yes, it's still a viable interpretation that whatever is being guarded needs protection by bashing mother's heads in with rocks... but homey don't roll that way.
Hard vs Soft Sci-fi (on the surface)
Lost confirmed their allegience to soft sci-fi, which was becoming clear, and that's not a bad thing... sure I love me some hard sci-fi, but I'm just trying to use up a lot of information I otherwise make no use of. Softer sci-fi often takes more opportunities with character, explores theme and idea, applies the general experimental ethos of sci-fi to personality and character. Ray Bradbury qed.
System to Channel Water and Light (underground)
As I say, though she says it's light and life, she's an ancient moron nutcase with no sense of science. It probably IS a strange quantum field generated by intense EMF, of course! Lost not only leaves these explanation open, inspire the with the Dharma angle, encourage them with MiB's references to the very smart men that like to know how things work... but also gives us wonderful images in which to fill this in. The underground tunnels are explained. I believe the MiB uses his smokey skills to manipulate waves of people that come to the island to complete his original plan, use the wheel (or another one), etc etc. He probably was using dharma too well to that end, and Jacob may likely be the direct one responsible for finally eradicating them.
Don't hate me because I'm calling the adam and eve reveal empty. And the cut backs to provey they thought of having the stones be pieces from a literal game rather than merely metaphors for that from the start... sadly I remembered those original scenes well enough, and one cut back would have been enough. In fact, I think it detracted from what was important to the narrative in that scene... Jacob has killed his brother, he has sided with a crazy murder, and looks more than a little bit nuts himself.
A Grade Theory
Anyone can be the final candidate now because it's a job for any old zealot-willing-to-kill. In fact, Kate (who is awesome btw), is now a prime candidate whoever crossed her off or not.