I still could not figure out what the sideways world was until the very end when Christian laid it all out: "How are you here?""I died too." Oh man.
And I think everyone online is on to something with that the sideways was a place for them all to "let go". And I don't think they all died close in time to each other: the whole wonky-time with the alt makes more sense this way. I know several places where people were trying to work out timelines for the alt and it would never jive: of course not, because it was all outside time and space. The only real-world reality this season was the island.
I found this episode hugely satisfying. I still have a million questions, but this was emotionally satisfying in a way I had not totally expected. As for Ben's fate, I think he just was not ready to let go of Alex and Rousseau yet. And I really wonder how Hurley ran the island! I really need more time to process all this, but it was a beautiful, crazy episode. Awesome TV. I will miss this show but I will now enjoy watching all the old seasons again!
I'm sure the DVD and the post-finale interviews will have lots of tidbits about unanswered questions. Like what was up with Ms Hawking seeing Desmond in his timetravel-flashbacks when he wanted to change the past (Faraday told her somehow?) and who built the big pendulum thingie (Faraday going to the mainland in the 70s?) and who put the cork in the island? and WHAT THE HECK was the smoke monster??? And how did Jacob's brother turn into that when he went into the glowy cave?
But the show really DID wrap up the character storylines. And they stayed totally true to their mantra: "dead is dead".