According to Lost executive producers Carlton Cuse and Damon Lindelof (via TVguide.com):
If there is a theme to Lost‘s sixth and final season, it might be “things coming full circle.”
“[In the first season, the characters] were running around the jungle, things felt intense and surprising,” the Hollywood Reporter quotes Cuse as saying. “We have a way that we’re going to be able to do that in the final season, too.”
The return of familiar faces — including the decidedly dead and presumed dead — will also come into play, with both Jeremy Davies and Elizabeth Mitchell set to reprise their roles as Faraday and Juliet. And based on the dramatic timing of Dominic Monaghan’s last-moment arrival on the dais, Charlie would seem a safe bet to (somehow) resurface as well.
“There’s a good chance you’ll be seeing many characters you haven’t seen since the first season,” said Lindelof.
Some tropes will be absent from Season 6. Time-travel is so yesterday, the producers indicated, and flashbacks/forwards are long gone. Instead, Lindelof said, “We’re going to do something different” to tell the final 18 hours’ worth of story.