Ab Arterno was the best episode ever in Lost imo.
As for the ending I have no idea, would Desmond really be the new Jacob if he wasn't even on the list after all its played up to be? That would also mean the numbers were pretty pointless. Widmore and Jacob seem to want the same thing, i.e. to stop MiB escaping, but if so, why did Ben turn the wheel to avoid Widmore finding it? Only thing i can think of is that Widmore had no idea Jacob was in trouble at the point of going to the Island on the freighter, he only wanted to exploit its properties. However, now he knows he has to stop MiB from escaping else he won't be able to harbor the energies.
I think the time lines are going to join up. Picture one time line and then it splitting into two, but still connected together at the point of the split a letter Y on its side. The two are going in opposite directions since "The Incident" in 1977 where they split, now the flash sideways show what would have happened if they didn't go to the Island but what happened would have always happened. This could explain the flashbacks Des was having in this episode in relation to Charlie and Penny. Some people think Des now knows exactly what to do and the reason he asked for the flight manufest was to get everyone back together and re-join both time lines, so it goes ----1977<>2007----.
One theory i have but is pretty obvious, Richard/Illana gets they candidates they are with, they team up with Widmore, kill some peeps, join forces to defeat MiB, Sayid dies, crossed off the list, they cross a few more off, candidate is selected and there is a final showdown between the candidate and MiB for the future of human kind. Then it could go two ways, MiB kills the candidate, reeks havoc, everyone dies. Candidate kills MiB, shows something really far in the future and the new Jacob sitting on the beach like Jacob and MiB were once upon a time, with a new MiB showing the world always has evil and it has to be kept balanced (in reference to the black and white stones on the scales, MiB threw the white (probably represents good) into the sea and therefore the black (probably representing evil) outbalances the good.).
But it could end so many ways!