Memory Alpha summary
"Today is a good day for style!"
Which means we've finally reached the point where the series has figured out how to present Worf, a character whose importance not just to the series but the franchise would grow exponentially. So basically what I said about "Manhunt" in regards to Lwaxana Troi. This was a season dedicated to figuring out the characters. Sometimes it worked exceptionally ("The Measure of a Man") and other times not as much ("The Icarus Factor").
In terms of lasting significance, "Emissary" may have the second greatest legacy of the season after "Q Who?" (which introduced the Borg) as it features K'Ehleyr, perhaps the best of the franchise's periodic efforts to feature "a former lover" (seriously, this is a whole Star Trek trope, and yes it's a fiction trope in general but Star Trek embraced the idea almost as enthusiastically as Space Nazis...and now we will end this parenthetical phrase...).
K'Ehleyr herself only survived to make one additional appearance ("Reunion"), but it completely opened up Worf's possibilities, not just because of the son they had together (Alexander, who would become a recurring character), but after "A Matter of Honor" (another second season classic, which actually featured Riker rather than Worf) stands as the birth of true Klingon nuance, a culture that flourished throughout the rest of the franchise until reinvention in the reboot era.
But aside from legacy, again, the episode itself works miracles for Worf, who until that point had languished under writers who seemed about as eager as Gene Roddenberry to have a Klingon in Picard's crew. Worf's own alienation was previously poorly defined and depicted, until he had another strong Klingon to play off against (and in subsequent Worf episodes, having other strong Klingons to play against proved to be a continuing source of strong material).
All of which makes the ending ironic, because Worf's not the only one who has a hard time being Klingon, his lover does, too, but they have to pretend to be exactly that, just a couple of regular warriors. But after this, it's much, much easier for regular Klingon warriors to populate Star Trek. For the first time, being Klingon means something other than cunning or prowess. And that is a very good thing.
four quarter analysis
franchise * series * essential * character