the story: Janeway dies. Repeatedly.
what it's all about: Fans who generally hate Voyager love this episode. The reason is pretty simple. Just look at my summary, above.
It's a baffling episode, arguably one of the most baffling of the whole franchise. By their third seasons, Next Generation and Deep Space Nine had taken fairly dodgy characterizations of their lead characters (Picard and Sisko, respectfully) into key selling points by figuring them out and giving them killer spotlights again and again. Janeway, like a lot of the third season, experiences an abrupt shift in Voyager's third season. While there's a lot right about the season, Janeway generally isn't part of it. The caustic Janeway fans remember can be traced to it, and "Coda" is kind of the epitome of this version of the character. Luckily, by the end of the season, "Scorpion," she's found a powerful new motivator, much like the series itself. It can't be overstated how importance Seven was to Janeway.
"Coda" purports to be a Janeway episode, and even features a likeness of her father, but the whole thing is a poor riff on the repetition concept featured brilliantly in Next Generation's "Cause and Effect." Literally Janeway dies. Repeatedly. There's some effort to make it matter to Chakotay, which is an irony of the episode, as it attempts to play off the version of these two that existed until the third season. If this had happened in the second season, it would've been done better, and it would have been better. This is just a hasty attempt to increase the episodic drama, which I think was the main creative mandate of the season. The problem with episodic storytelling is that it's inherently hit or miss. Given a whole season to fill, there will never be enough time to polish every story.
The most egregious thing about it is that the Vidiians technically make their last major appearance of the series, and their part in it could really have been filled by any aliens, which is basically...exactly the opposite of a decent Vidiian appearance (heh).
franchise- Not recommended for casual viewers. series- Not recommended for fans.
- character - Your best bet is to try and decide whether or not this constitutes an adequate Janeway spotlight.
essential- No, it's not.