If much in the world were mystery the limits of that world were not, for it was without measure or bound and there were contained within it creatures more horrible yet and men of other colors and beings which no man has looked upon and yet not alien none of it more than were their own hearts alien in them, whatever wilderness contained there and whatever beasts.
-- Cormac McCarthy, Blood Meridian, p. 138
Let's start off with something positive. I'm hard-pressed to think of a better filmed death than Jack's. As someone who's experienced the passing of a loved one after a arduous, painful struggle, I found the serenity in his letting go pitch perfect. Undoubtedly, it's one of Lost's best scenes, sharing a similar timbre with my other favorite death scene, that of Twin Peaks' Leland. Going back to their comment on one of the early blu-ray extras, the showrunners Damon Lindelof and Carlton Cuse knew exactly how they wanted to end their story. According to actor Matthew Fox, they told him the fate of his character during the first season. Unfortunately, what wasn't so planned out was how Jack would get there. "The End" leaves us with five seasons of dangling plot threads that don't add up to much. Instead of having all of that leading to Jack's death, this sequence is constantly interrupted with a bunch of treacle involving almost all the main characters, both alive and dead, meeting up in a church in the alternative "sideways" world to head off into cliché, the afterlife's white light. Evidently, the finale needed an extra half hour just to include a bunch of flashbacks (previous seasons instead relied on audience intelligence) and all the hugging and smiling that goes on in the church. Thus, through parallel editing, the best and worst are presented simultaneously.
The apologia began well before the finale aired, with the showrunners preparing the line of argument by which the most ardent fanboys could defend the ad hoc denouement. Somewhere along the way Lindelof and Cuse must've realized what a non sequitur the sideways timeline was going to be, so they created a preemptive defense that went something like this: This was their story, and they were going to end it the way the saw fit, namely by focusing on the main character arcs and answering only those questions that pertained to this goal. It wasn't their job to spoon-feed us all the solutions to the narrative riddles they'd created. (From what I hear, those wishing to be babied will have to buy the box set, which will include an explanatory extra disc.) And this condescension is pretty well followed in Jeff Jensen's blog, propaganda central for the show. I also heard something similar from friends who were more fulfilled by the ending than I. Isn't that what I was wanting, for an air of mystery to remain?
Well, let's get something cleared up: mystery and plot resolution are not mutually exclusive within a narrative. Fallaciously assuming the contrary is exactly the basis on which Lindelof and Cuse attempt to rest their defense. It's helpful here to consider Noam Chomsky's distinction between a problem and a mystery. The former is a question to which we have a reasonable expectation of an answer somewhere down the road (e.g., who killed Sally?), whereas the latter exceeds all current constraints on our thinking, inviting speculation and/or faith (e.g., why is there something rather than nothing?). Fiction isn't scientific experimentation, so a writer can, of course, play about with what's a narrative problem or mystery. A major problem with Battlestar Galactica was the reduction of all of its mysteries to a jerry-built deus ex machina explanation. To its credit, Lost doesn't have an episode of a talking head revealing the grand design. But its creators, not wanting to do that kind of story, seem to believe mystery alone freed them from basic plot construction.
It served the show well to keep the nature of the island and its properties a mystery (ontologically ambiguous between scientistic explanations of electromagnetism and pure magic, the more muddled attempt at questioning the distinction between free will and determinism, as well as the island's ambivalent status as an allegory for the foundation of morality). In finally committing his life to this mysterious island, Jack provides an example of what's at stake in fidelity to a cause, where there is no clear cut contract with numerous contingencies laid out in fine print. His conversion is a far more convincing case for the need of faith as revealed through grace than you'll ever see coming from stories told by conservative Christians (e.g., The Passion of the Christ). This arc alone is, to me, justification enough for watching the entire series, but it doesn't excuse the faulty construction of the final season.
If one introduces a narrative element, regardless of whether it's a place, character/group, or even motif, and regardless of whether any of those is supernatural or natural, the audience has a reasonable expectation that it'll serve some purpose to the story unfolding. That is to say, its function is as a problem, not a mystery. And I'm not talking about certain stylistic choices, such as film's shot construction, color palette, or the look of actors (although they can and do have narrative implications), but plot elements (and by 'plot', I mean what the formalists call fabula, an element's status in the cause and effect chain, if you're the type who considers such things). So, when season after season, the fate of Lost's characters is interwoven with the shadowy organization known as DHARMA, or what's left of their presence on the island, expecting some payoff to that isn't a case of wanting to be spoonfed a conclusive interpretation of what it all means. Similarly, when a major character like Juliet is introduced via her role in attempting to solve why babies can't be conceived on the island and that element is tied into numerous other subplots (such as the kidnapping of Claire's child), the audience has a reasonable expectation that all this baby stuff is somehow more significant than just giving the writers a baroque technique for introducing a character. Instead, those threads were cut in favor of introducing the sideways timeline, which then became the primary plot to be resolved in the finale. Obviously, the creators didn't consider wrapping that up as crass demystification.