As an episode in general, any one ever where 1) someone/something messes around with the timeline, screwing up a bunch of stuff 2) they go back and do a bunch of stuff to fix it, timeline returns to normal, fade to 3) end of episode, everything is as if nothing ever happened, all characters, in actuality, DID NOTHING, and NOTHING ACTUALLY HAPPENED
Every time I run into this episode in Star Trek or any other sci-fi, I want that hour of my life back. Like, why did I just watch all of this, if literally nothing happened?
They also had a second one (the crossover) where things were 99% the same but 1% different at the end and they're just like "meh, that's close enough."
Perhaps you aren't familiar with the idea of episodic television? All episodes of TOS/TNG are episodic. This means that with very specific exceptions that are related to the over araching story, if there is one, nothing ever happens during the episode that will affect future episodes. It is literally the design of Star Trek from the begin. It's why the episodes open with a nonsense star date.
Actually, that's not true, as established in the novels and canonised in SNW last series, the timeline is in constant flux with certian events having to happen but moving due to interference. Hence why the Eugenics wars were meant to be in the 90s in TOS, now they happen post 2020 in the current timeline.