Lost: stumbling to a conclusion

So I didn't like the last episode of Lost - "Across the Sea", the one that that was purportedly going to fill us in on where Jacob and the Man in Black came from. Two of my friends, though, liked it well enough, and supplied the following comments:

• Alex "finds it incredibly amusing that Lost viewers get disappointed when 'nothing was made clear,' as if that was something that has *ever* happened. From where do they derive this expectation of clarity?"
• Geoff writes that "It would not be Lost without the messy. If you have not come to enjoy the messiness, I am surprised you still watch the show."
  

These are fine points, but I don't think that either really addresses my problem with the episode. And simply, it was this - if this is the big mythology-information-dump leading up to the finale, it should have left me certain that I know what the stakes of the final showdown between Jack's group and the Man in Black are. And it didn't.

Sure, it told me that Jack and MiB are brothers, that the mysterious power source at the center of the island is a light, that MiB simply wants to leave for the sake of leaving... but these were hardly the burning questions that I wanted answered. What I felt that I needed to know was what would happen if MiB were to leave, and why he needed to be stopped. (If, in fact, that needed to happen.) And not only is the 'why' not clear to me, but MiB is made so sympathetic - and Jacob's mission is made so doubtful due to the unreliability of the character whose job he has taken - that I feel less certain that MiB has to be stopped at all.

I should add that Geoff uses gnosticism to provide a plausible answer to my most burning questions. This is what he writes:

the energy at the center of the island is the light of creation, or something like that. The Smoke is the opposite number, split off when the light was disturbed by someone corrupted by men — this is pure Gnostic mythology. Somehow the smoke is or has the light now and if it leaves the island everything goes out everywhere.

Okay, I can buy that. But even if Geoff is right, that particular thought never occurred to me until I read Geoff's review. I didn't even notice that the light went out in the cave, nor did I think, when it was first pointed out to me in an article elsewhere, that a) this would necessarily mean that MiB now has/is the light, and b) the world should end if he leaves with it. If this is true, it actually becomes the entire point of the show. And if I need someone's blog or a thorough understanding of gnosticism to point out something so fundamental to my understanding of the show, then it hasn't been made clear enough.*

* [What's especially annoying about this is that the connection made between 'Adam and Eve' from season one and the bodies of Mother and Brother was drawn in the most hamfisted and patronizing way - with horribly incorporated cut-scenes. Why be so painfully clear about such a minor detail, when you so badly explain something so much more important with the creation of the smoke monster and disappearance of the light?]