Having slept on this weighty matter, I have decided that Lost's makers were very smart to end it as they did. There was no way they could resolve all of the pseudoscientific mysteries satisfactorily, and neither was the mythology they had created cohesive enough to be wrapped up tidily, so they opted for sentimentality. They gave the viewers a bunch of happy endings, which probably left more people with a better taste in their mouths than a lot of half-assed explanation would have done. I mostly find that when mysteries are explained, there's a letdown, sort of like the slump during those hours after the presents have been opened on Christmas morning. Even if Cuse and Lindelof had been able to check all the boxes by all the unanswered questions--and I don't think they could have, because they themselves had no idea what boxes to check--some people might have felt the fussy glow one gets after completing a task but that comfort would have been cold compared to all the easy emotions evoked by all the soppiness. Where Cuse and Lindelof screwed up, I think, is promising--or at least implying--that everything would be tied up with a neat bow. That is what has caused so many people to feel a little bit as though they've been duped.
But, hey, it was only a TV show.