[The Rick]

Quoted from an article in the USA Today. I think they sum up what happened nicely:

As it turns out, those now-beloved characters weren't just lost in the real world of the island. They were also lost in what many had assumed was an alternate "sideways" universe triggered by last season's atom bomb but was actually a gathering place for the dead as they wait to move on.

In many ways, the finale was designed to reaffirm what producers Damon Lindelof and Carlton Cuse have told us for years: The island exists; what happens there matters. If the light (which looked far less cheesy this week than last) had stayed out, the world would have ended.

But they also were reminding us that ultimately, for individuals, saving the world only delays the inevitable. We all die.

So in some ways the 2½-hour finale was two journeys, both centered on Jack, each illustrating the themes of individual redemption and group responsibility. On our world, he saved the island, handed the guardian job to Hurley, and died. (For the record, Kate, Sawyer, Claire, Miles, Richard, Lapidus and Desmond eventually left the island; Hurley and Ben stayed.) In the other world, the post-life purgatory where "now" does not exist, he was the final piece that reunited the characters and allowed all to leave — a reawakening of memories, theirs and ours, any fan had to cherish.

http://www.usatoday.com/life/televis...T_N.htm?csp=hf