I think we should process the Lost ending, not as an audience, but as the losties themselves. Let me explain.
For me at least, watching Lost was about watching the characters. They were so well written, they we as the audience felt like we knew them personally, that they existed, and we were connected. When something horrible happened to them, we felt that. I'm not talking about the supporting cast (miles, lapadius, widmore, ect) but the losties themselves (Jack, Kate, Hurley, Sawyer).
So we are one and the same with the Losties. Sayid doesn't know how he was resurrected and neither do we. Jack has no idea who created that cork or what exactly smokie was and neither do we. We are on the same playing field as the characters themselves, and the connection over the 6 years has grown stronger because of that. It would have been completely out of character for the show to just bombard us with answers during this final season, when even the losties had no idea how exactly things were happening, just so that we would know.
The most important part of this, and why the finale really worked for me, is that at the end, I felt the same relief that the main characters felt after they remembered. They had found peace. They completed their destiny. And now they could move on. Do we know why the island existed? No...but neither does Jack, Desmond, Hurley, Kate, Sawyer, Jin, Sun, Claire, Locke, Ben, or Charlie.