This episode can be split into three parts. Let's begin.
Jin time-travelling with Rousseau and her team is one of the most exciting and mind blowing moments of Lost. We get the Smoke monster, we get the Numbers, the infection, the Temple. And in my opinion, the scene where Montand's voice is heard from the tunnels is pretty darn important because I honestly believe that wasn't Montand (I'm not going to spoil the mystery, I'll give a hint: MiB). Oh yeah, Smokey is the security system of the Island. Really? Can't wait to see how that plays out in the second part of the final season. And we move to...
Jin reuniting with Locke and co. was expected and it started the Sun/Jin hide and seek game that got boring 15 episodes later. But nevermind, the trip to the Orchid station was emotional, Charlotte dying and all. Her 'This place is death' line does make much more sense after some episodes of season 6 (again, not spoiling).
The whole they-have-to-go-back-in-order-to-stop-the-flashes story somewhat culminates in this episode and to this date, I still have no idea why they had to go back (possible spoiler: except if it weren't a grand scale manipulation for Locke to come back to the Island as a dead man along with the remaining Candidates).
Christian again was a great surprise and it only deepened the mystery of Shephard Senior. I've got no ideas as to what is his agenda, is he dead or alive, is he just another manifestation of the Smoke monster (ok guys, we've already known Smokey could transform into dead people) and what does he have to do with Eloise Hawking. As for the future, I hope we'll get answers regarding the well and the wheel. It'd be lame if they didn't explain how was time-travelling possible. With the mention of Eloise Hawking, we come to...
Jack, Ben, Sayid, Kate and Sun in one place. Kate was hysteric as always, nothing to say about her. These scenes culminated with Ben, Jack and Sun meeting Desmond in front of the church where the ever mysterious Eloise Hawking dwells. It's time for Losties to come back home.