You knew, given the way the writers on Lost think, that they were going to find a way to put a flashback and a flashforward in the same episode, which is exactly what happens here, though they don't show their hand to the end (and frankly, by the last scene, you're praying that they're not going to). And it makes a horrible kind of sense that it would involve our favorite couple, Jin and Sun. A lot has come between them over the past three seasons and in all the flashbacks of their history. But in 'Ji Yeon', they seem to finally find a way to get past it, only to end up separated by the largest divide of all. But let's take this step by step.
Sun and Jin have now realized what everyone else has--- that this freighter does not mean rescue--- and now they've decided, despite the risks, to defect to Locke's camp. (As it turns out, that decision could've gotten them killed right then, but then every day's a picnic on the island.). But Juliet, in a move that seems more desperate than calculated, breaks her oath, and reveals Sun's affair to Jin. Because Jin by necessity wears such a stoic mask, it's hard to tell just how devastating this news is to him. But we get a very good idea when he goes fishing with Bernard, who we haven't seen in a bit. Bernard then does something that no one else on this island has done--- he reveals something secret to another castaway, in this case, telling Jin about Rose's cancer and how she believes that she's cured. He then says the reason they stayed with Jack was because he was a murderer, and that it would be bad karma for them to stay. It's hard to know how much Jin understands, but we know from his own words (way back in 'Exodus') that he believes being on this island is his punishment for his cruel behavior while working for Mr. Paik.
So Jin does one of the most beautiful things of all the characters on the series--- he forgives Sun for her affair. Hell, he even tries to wear some of the guilt as his own, because he knows what a horrible man he became. (Of course, he doesn't know why he ended up working for Mr. Paik, but that's beside the point). So he tells Sun that they will try to find a way off this island, and they will escape.
Now admittedly, there've been signs that the flashes involving Jin and Sun were of different times--- Jin had a monster of a cell phone in his flashes, Sun's refusal to let the doctor remove her wedding the ring, the way the doctors seemed to know by their celebrity status that Jin was dead--- but even knowing all that (or, for that matter, knowing what's going to happen in Season 5) doesn't mean that the final scene is any less gutwrenching. Seeing Sun reduced to her more devastated ,ode, even as she holds Jin's child, is one that is heartbreaking. What makes it even sadder is that after the birth of her child, the gentle and compassionate Sun we've come to know and love, will all but disappear. In her place will come someone crueler and colder, someone--- well, let's be honest--- is a lot like her father Right now, we're not sure why, but there's got to be a reason that Hurley was the only member of the Oceanic 6 to come see her after Ji Yeon's birth (and why he was so glad not to see any of his friends). What we're not sure of is when and how Jin died, and if the Oceanic 6 are lying about his dying in the crash.
Speaking of which, we now know who they are---- Jack, Kate, Hurley, Sayid, Sun, and Aaron. The problem is this leaving a gap in Jack's story big enough to fly a plane through when he said at Kate's trial that only eight people survived the crash. How does that make Aaron--- who must have been born before the survivors were rescued--- one of the people who survived. Yes, they say Kate managed to cut him off at the trial, but I'm not entirely sold on that either. This may be a continuity error that never gets explained.
Meanwhile, on the freighter, Sayid and Desmond are learning that things are actually a lot worse than they thought. They meet the captain of the boat, who seems particular nasty (but then, maybe he's just a little concerned about how the members of his crew are dying right and left), and who seems more than willing to tell them what they want to know. He reveals that this is Charles Widmore's ship (I don't know how Desmond managed to maintain even a moderate level of calm when he learned this) and that the wreckage of flight 815 was found on the ocean floor. Then he reveals that they found 324 dead bodies on the freighter, and that they believe the man responsible is Ben. Unfortunately, all of this is thrown into disbelief when they received a note that says "Don't believe the captain." So now Widmore is saying Ben's responsible, and Ben is blaming Widmore (though they don't know it yet) Both of these men already seem like monsters, but which ones do we believe?
Oh, and we finally find out who Ben's man on the boat, though honestly, we should've figured it out a lot sooner. Considering that Harold Perrineau has been listed as a cast member for the last six episodes, but we haven't seen hide nor hair of him--- even in the flashforwards. So when the doc calls for Kevin Johnson, and we finally see that this is in fact Michael, it's probably the biggest anticlimax this series will ever produce. What makes it even harder to believe is why Michael--- who sold his soul to get off the island--- would be willing to do anything to get back here. I will say this, though: From what we see of Michael's face, he looks like he hasn't gotten a decent night's sleep in a very long time.
Well, we're getting answers but they're not very neat ones. But that we can live without for now. What is more pertinent is that it appears that death is going to separate our favorite couple on the island. And that even that might not be enough to keep them apart.
My score: 8