It's the moment of 9-year-old Kes' death. She has no memories of her life, not even of the daughter and grandson by her side. But then she flashes to another time and place. She's hopping backwards through time, and must explain the problem to the crew of Voyager and hope they can help her escape.
To dissipate any tension right now, I don't think this is Top 10 Voyager; for me, it would barely make the Top 10 I've seen so far in this rewatch, and I still have more than half the series to go. But no, it isn't bad, and yes, it is fun. This is Voyager's version of a "Future Imperfect" or perhaps a "Children of Time" -- the more you're invested in the characters, the more fun you find it to get a tantalizing glimpse of what their future might be like. I myself am far less invested in the Voyager characters than those of The Next Generation or Deep Space Nine, and so, predictably, I'm less swept up in this story.
But it is a clever into "time travel problem" that Star Trek hadn't presented before. (And it should be pointed out, this episode was made before the movie Memento -- which, while not a time travel story, is famously premised on a backwards narrative.) Kes is a particularly fun character to have hopping backward through her life, since from the day we've met her, we've been told exactly how short a time that life will last.
The episode effectively introduces new characters and makes us care about them in a short time. Kes has a nice rapport with her grandson, and a good scene with her daughter (easing her anxieties about parenthood). We're given plenty of fun "what ifs," from the delicious awkwardness of Harry Kim as Tom Paris' son-in-law, to a Doctor with hair and a name, to a Captain Chakotay, to Neelix as a full-fledged security officer (now that's science fiction!). More fun fan service happens in a brief flashback to the pilot episode, and then a glimpse of a young Kes before even that. Most importantly, the relationship between Tom and Kes does work to give some emotional stakes to the whole.
But if you have any doubts that this episode is really just here to have fun, that's confirmed by how little the premise holds up to any scrutiny. We're told why Kes is traveling backward through time, but given no rhyme or reason to how long she stays in one place or why she jumps as far as she does each time. (The answers to these questions: she goes where/when the plot needs her to, as it needs her to.) There's also no explanation for why, when she reaches the beginning of her life, she just starts going forward through it again like a yo-yo. Plus, to make sure everyone knows this was "just for funsies," we're explicitly told in the end that the future Kes saw is just one possible future, now likely to be different.
Other observations:
- The old age makeup on Kes in the early (later?) scenes is reasonably effective, especially when you consider that Jennifer Lien was in her early 20s at the time.
- There's speculation that Old Kes is experiencing "morilogium." More "Elogium?" Please no.
- Tom Paris at one point mentions the past deaths of Janeway, Joe Carey, and B'Elanna. Forget how odd it is to be bringing up a minor character we haven't seen since season one. It's truly weird to name anybody in between Janeway and B'Elanna, since we see their deaths later in the episode, and they happen at exactly the same time.
- Though most of this episode's future never comes to pass, the mention of the "Year of Hell" and the Krenim is something the show would revisit later. The writers were actually planning at this time for what they thought would be their season three cliffhanger and season four opener... though subsequently the decision to bring a new character onto the series delayed all that.
- Kes has a new hairstyle starting in this episode, and while you might expect "oh, that's only for the future scenes," the long hair is actually here to stay. This was reportedly because Jennifer Lien had developed an allergic reaction to the makeup of her Ocampan ears, and the long hair was a workaround so that she would only rarely have to apply it.
"Before and After" is reasonably fun. But like I said, it's probably more fun to someone who rates Voyager more higher in general in the Star Trek canon. I give it it a B. (The episode, not the series.)