As to the Season Five format:
We've basically already seen the important events of the Oceanic Six's three years. So I think that the "present" time will be Three Years Later, showing the O6's efforts to return to the Island. Meanwhile the "flashbacks" will show Island events of the past three years. Then the S5 Finale will be the O6 arriving at the Island. And S6 will be them doing whatever they have to do on the Island.
I agree. The producers have said that season 4 is about how they got off the island, season 5 is about getting back onto the island, and 6 is about what happens when they get back. The present day events will follow the six as they group up again and head on back while the flashbacks are what the "very bad things are." The finale next year will be Locke coming back to life and something wacky happening shortly after.
As for this finale, I thought it was excellent, if only because Desmond and Penny's story had some closure. Of course, this means that something awful can happen to them now, as Ben's revenge story will need resolution.
Other little things I liked:
-Hints about Charlotte's past, especially her being born on the island. I don't think she's Annie--mostly because Ben shot her early on in the season--but finally she has something interesting going on with her. Man, talk about being signed onto a show and given absolutely nothing to do.
--Juliet on the beach with the rum. I feel so bad for her, every time she tries to get off the island and just can't. I think she's gonna be the victim of some of the "bad things" next year, since there's nothing between her and Jack anymore.
--Seeing Walt again briefly.
--Hurley seeing even more dead people (Mr. Eko shout out!)
--Ben fighting back tears as he turned the wheel, knowing he could never come back.
--Sawyer continuing to be the biggest hero on the show, weirdly enough.
--Sayid getting Hurley to a "safe place."
--Claire popping up unexpectedly.
--The "bloop" sound when the island disappears, funny touch.