What do you think about
All Our Yesterdays as a potential replacement 'finale'? Sometimes I do think its hardcore exploration of the 'big three' as characters (seperating Kirk from the group and forcing McCoy and Spock into a survival situation) feels more fitting as a finale-of-sorts than
Turnabout Intruder, which as you say feels a lot like it could have been any old episode in the middle of the season.
I consider All of Our Yesterday's to be a finale worthy of TOS the series.
Correct me if I'm wrong, but...doesn't "All Our Yesterdays" have a "later" stardate than "Turnabout Intruder?"
(Interesting note--when I first got the three seasons of TOS on DVD, I'd made it a point to watch them all in order of
stardate. It actually held up pretty well, really.

)
ENT ended with Demons and Terra Prime. TATV? I don't know what you mean.
This...except Terra Prime kinda has a downer of a final scene, right? Perhaps with a more "uplifting" epilogue...?
Anyway--rankings; well, let's see
...as finales, not necessarily
as episodes unto themselves....
"What You Leave Behind"--full stop. It was a true "closure" to the series.
This may seem odd, but--I'd actually put VGR and TOS ahead of "All Good Things" (but not by much--practically a three-way tie). Say what you will about it..."Endgame"
was a conclusion to the main conflict of the show--getting
home. I
would have loved the mains having a final scene together, talking about what they'll do next, remembering Kes and, yes, Neelix...and perhaps Janeway toasting them (with coffee, of course), and the future. Still...can't have it all, can you?
"All Our Yesterdays", for the reason
Lance noted--but with a caveat similar to my thoughts for "Endgame": I'd have loved, when Kirk, Spock, and McCoy are reunited, have an emphasized moment where our trio note how it's good to be back--all three of them. In many ways, our trio
were the emotional "backbone" of the series--and it would've been great to have them acknowledge their deep friendship, once more.
"All Good Things" has a nice bookend with the big-time references to "Encounter At Farpoint" (and a look at a possible future)...but did it really provide much of an emotional "wrap-up" for the series? Um...not really. Except maybe between Q and Picard. I mean--I love poker! But...was that final game REALLY much of a wrap-up? Um....
What I remember of "Demons" and "Terra Prime" (it's been a while)--it's a great finale
in the sense of its BIG "
This is how the seeds of what would become the UFP were sown." Still, a good finale, as I noted above,
must have emotional closure for the
characters, too. I...don't recall much, there. Apparently, all the emotional stuff was reserved for TATV.