Just going to copy-paste my quick thoughts from my reddit post;
My reading on it was slightly different than other peoples.
I took when Cooper saw Naido (and the permanent overlay of his face over the rest of the scene) to be his own realization of the false reality he had been experiencing. Him coming out at Glastonbury is him walking out 25 years later, as originally intended (whatever happens in those 25 years doesn't really matter). While in there he tried the timeline shenanigans in FWWM and in The Return, and on his pursuit to fix things, ends up once again trapped between two worlds (in this case, seemingly in a different time and a reality where Laura is alive .. but isn't .. ala Philip Jeffries "What year is it?").
Even the framing in Part 17, where you see essentially every major side character lined up like a roll call, it feels very unreal.
I do hope we get more. But, this is a similar downer of an ending to me that Season 2 has, though, quite not intense (more .. "Dale Cooper is sort of a failure"). This one at least can play like a depressing ending moreso than Season 2's straight laced cliffhanger.
It does make you wonder the wisdom in dragging out so much of the stuff in the first 17 parts when the table is going to get flipped in part 18 anyway (and leave a ton of loose ends in .. that world of Twin Peaks, such as Audrey).
I suppose on the plus side, if they do more they might not have to work around some actor's deaths as much, given that the world of story is very different. But, then again, wouldn't they have potentially written themselves into a very similar box as this season (you have a potentially decades long gap and have no idea on the status quo on major side characters)?
A ton to unpack in this episode.
I'm also a little bummed at just how perfunctory Dale Cooper's return to Twin Peaks was. I'm fine with not over indulging in nostalgia, but, it felt a little bit like Lynch really didn't care about Coop's return to Peaks itself, as it was kind of a formality.
Also, the potentially "The Return was mostly a dream" makes some sense to me, as I think BOB, the apparent pain and suffering of all mankind, being punched by a kid with a rubber glove feels like the kind of overtly optimistic dream logic one can have.