I rather liked it, and not just because I was right all along.
In that, the show was about a limbo of sorts. It was clearly about that in the first season, and clearly about that in the last. That they shifted the "location" of limbo from the island to a sideways universe does not change the story --- especially since they only thing they were able to "wrap up"
was the limbo storyline -- while there was no wrap-up whatsoever of The Island.
That didn't bother me. I don't much care which question is "answered" and which mystery is left unsolved. I like that the finale engendered a lot of conversation and theorizing at Heidi and Tom's most excellent Last Lost party. And unlike some of the recent episodes that were supposed to be emotionally affective (but did not hit me as such), this one packed a punch of strong feelings for me.
I was a little meh about the demise of anti-locke, and of course revealing "the light" to be yet another set-piece ("the cork") was no revelation at all. But these were quibbles in an otherwise rather fine episode. The Christian religiosity certainly didn't bug me - - limbo and purgatory are essentially Christian concepts.
Um, one question occurred to me - and maybe I just missed it: Did they show what became of Island Desmond after he was pulled out of the Cork Cave? I mean, Ben and Hugo team up for Lost, the Animated Series. Sawyer, Kate, Claire, Richard, Miles and Lapides escape on the plane. Jack dies. Did they ever show Desmond again? Did he just wander off into the woods? Did he have a delayed reaction time-shift that he was expecting?
I think the limbo matrix co-created by the Losties would have seemed more plausible if it was just the tight group of Losties who had been through so much together. Bringing in Boon and Shannon and the neighbor's cat was a little silly, imo. So was Sayid and Shannon getting together for the afterlife, as if she were the love of his soul, instead of the quick fling they once shared (which, had it not been for their touch-flash, I would not have even remembered!)
Quibbles and bits. I liked it. Christian Shepard's final appearance was a bit more powerful, experiencing it with two other people who have recently lost a parent. The writers couldn't have scripted that, but I think it infused the ending with a certain oomph for us.
A surprising thumbs-up from me.