I just described the episode to a friend, and I think these two words described it perfectly.
It set out what it intended to do, it ended the threat of the smoke monster for good, it answered a few questions, and it gave everyone - including characters we didn't think would ever have them - their happy endings.
So yes, there's a lot of satisfying there.
Was it perfect? Gosh no.
Did it answer everything? FUCK no.
No way it could.
But it did what it had to do. And so... Annoyingly satisfying.
The final scene was perfect. The final scene HAD to be that, no questions asked. It ends as it began, and the circle of life is complete.
I literally welled up when Hugo saw Charlie and just got this HUGE grin. Seeing his old friend again, alive and well... Gods, it felt so good.
Most of the realisation scenes got to me good.
And thank the gods that Locke, The REAL Locke, got a few more moments back with everyone, and to say a few words. That made me very happy.
I'm also personally squeeing at seeing Maggie again, but that's probably no secret. ;)
So, what was the 'alternate timeline'? I like to think of it as the proverbial life flashing before their eyes, and this place exists in some limbo place that is always there. Waiting for everyone to come and be there in their time of ending. I twigged onto them being dead somewhere around the halfway point. I love that the creators got to do the 'everyone is dead' thing, while NOT having the island be heaven, hell, purgatory, or whatever like a lot of early theories said, and so they could deny that and still pull this off.
They also did a really great job of playing with our expectations of the alternate universe being just that, created in the Incident as a true alternate timeline. Still feel they wasted a lot of time there though, and I wish we had gotten around to some stuff we were seeing tonight much earlier, on both sides of the timelines. If a lot of the stuff tonight happened midway through the season, or we had one more season to go, I really think some things could have been better fleshed out.
I might come back to this later, I'm still processing and want to rewatch it again.
Mostly, I'm happy. There's more I would've liked, but I can live with this, yes indeed.
I don't think it quite lived up to my "They'll pull this whole thing together way better than BSG did" but they did a good job. I'd still put it a bit ahead of that finale.