Very good premiere. A few quick questions and observations:
--Why didn't Jack seem to recognize the name "Jacob" when Hurley mentioned it?
--It's interesting that the Smoke Monster identified itself as the protector of the Temple when in possession in the 1970s of one of Rousseau's shipmates -- it was also ID'd as a security system I believe on the Blast Door Map -- but the denizens of the Temple are working now to protect themselves from it. Also interesting that Smokey as recently as 2004 was at the service of the Others, i.e. when Ben summoned it to kill Keamey's men. Maybe it was contractually bound up to the point when the Man in Black found the loophole?
--Is the pool of water that Ben accessed under the Barracks in season five's "Dead Is Dead," apparently in an attempt to summon the Monster (it failed, presumably because Smokey had already taken on Locke's form and was therefore out of the house on business), connected in any way to the spring of life inside the Temple? Was the fact that the spring wasn't clear due to Smoke Monster activity somehow?
--The fact that Christian Shepherd's coffin disappeared strikes me as the most ominous sign about this "sideways" reality. There's an assumption that it was lost before the plane took off, but maybe it was sucked off the plane to the Island during the turbulence? Maybe Desmond was too? The Man in Black wants to go "home," which I take to mean off the Island. Maybe in this alternate reality he has already succeeded, perhaps when the Island sunk. By doing all the things they did, the castaways brought about the end of the world predicted by the Valenzetti Equation by creating a reality in which this destructive force is unleashed. Bigmouth has speculated about the importance of baby Aaron. Maybe in this reality the wrong person, a Bad person, adopts the baby, as Claire's psychic implied.
--We saw in the previews that fake Locke looks to create an ally in Sawyer, who is still embittered by Juliet's death, a la the emperor and Anakin Skywalker. Perhaps Sawyer will pull a long con on the Man in Black and double-cross him?
--Given what we've seen of the merry band of Others at the Temple, was Ben ever really their leader? Or was he simply the lieutenant in charge of the outside Others who roam around, drawing the attention of Dharma and other intruders away from the Temple?