Consider how she began the season, Janeway really needed a break, and that's exactly what she got in "Fair Haven."
A lot of fans latched onto the later episode "Spirit Folk" as indicative of what made the season so generally appalling, and joked that the Captain had a romance with a hologram, but actually watching "Fair Haven" is a strong argument that these sentiments are spurious at best.
In the early seasons, Janeway had a fiance in the Alpha Quadrant and a budding romance with Chakotay. Both were subsequently taken from her, and the strain of the voyage was displayed in episodes like "Night," and the sad fact is that she probably suffered the most out of everyone for the decision she made in "Caretaker." "Fair Haven" represents the first break she had in six seasons, and is an appropriately complicated tale for someone in as complicated a situation as Janeway.
I won't go so far as to say it's essential viewing, but for both the season and the series, it wouldn't have made any sense for it not to happen. For Janeway, it's a defining episode, to be sure, and I've said elsewhere, the whole season seems to have been dedicated at the very least to settling thorny issues from the past and preparing everyone for the conclusion. Yes, you can skip this one and still follow the thrust of things, but not if you want to know or care about Kathryn Janeway.
franchise * series * essential * character
Memory Alpha summary.