Ok more coherent thoughts now. I can already see how this ending is probably going to be divisive and to an extent I understand why. Before it aired, I wasn't keen on the idea of the show ending like this. People don't like endings where the found family go their separate ways, except that isn't really what's happening here. And I think the way they did it was perfect.
Alison has come in and completely turned these ghosts' unlives around. She's given them purpose, connections with the outside world and each other, and above all a lack of boredom. Boredom is one of the main existential challenges the ghosts face. Alison isn't abandoning them to what they had before she came - she's leaving them with the tools to actually live rather than just exist after her.
And she's not gone forever! Families don't have to live together to be family. She comes back and visit them regularly! Maybe it's just because I moved out from my parents' in the last few years and I'm back for Christmas, but her being a regular at the hotel, coming back and visiting them at least every Christmas (maybe more) was very moving to me. Just because she's moved out doesn't mean they're not still family.
Having it become a hotel is a nice bookend and I bet it's improved the ghosts' quality of unlife a lot. As I said, their biggest challenge has always been boredom. A hotel/golf course probably isn't at all boring. How many affairs do you think Julian has watched? It's perfect for them, with all the people coming and going. I bet they even stage the odd haunting for fun. A constant, varied existence is a great fate for them.
Ending the episode with the plague ghosts was PERFECT. Obviously, it was great to see them again and it was hilarious as they always are. But it struck me just how much this decision has improved their situation - they've gone from dingy cellar to sauna. And that's the analogy of how much things have improved for all the ghosts.
Change is scary. It's sad when things come to an end. But sometimes it's for the best. And an end doesn't always mean a closed door.