That was a spectacular episode and revealed many things. I don't want to talk about every actor seperately. All of them had great performances, especially Sawyer.
First of all i'd like to focus on something that Hauking said, a few episodes before: "If you don't bring EVERYONE back, the result will be unpredictable".
When Sun left the island, she was pregnant to Ji Yeon. So, Ji Yeon should have returned to the island with Sun. That's the reason Sun stuck at 2008, and did not go to 1977. It's the unpredictacle result, that Hauking mentioned. Ben din't go to 1977, because he can't meet himself.
The simulation of flight 815:
- In 815, the plane seperated in two parts. We had the main and the tail section. In 816, we have also two groups.
- The 2nd pilot of 816, dies during the crash, like the 2nd pilot of 815...
- Jack is the "new Locke". The new man of faith.
- Sawyer is the "new Jack". The new leader.
- Sun is the "new Rose". She carries her wedding ring and waits for the reunite with her husband.
Fate changes (a 2nd universe):
Hurley's references about the Purge, are very important. Faradey has said that we can walk the road, but we can't build a new road. That's not true. Sun, Ben, Locke etc... live in 2008. We're sure about that, because at the end of the scenes, we saw a "30 years before" message.
But a lot of things has changed in the future:
- When Frank entered the island, we heard the numbers "8 15 16..". So, Daniel never recorded her signal.
- At the barracks, we can see Dharma sign-boards. The houses seem abandoned for many years. The others never lived there, and probably the Purge never happened.
- The dock is undamaged. So, Locke never put C4 and he didn't blew up the submarine.
I'm too confused right now, but that's the point of LOST. :P