What You Leave Behind is the end of an extraordinary show and one of the best series finales I've ever seen, to a series I've immensely enjoyed throughout its seven season run. 170+ episodes have led up to this point: the Dominion War is coming to an epic conclusion... and the Emissary's final test is at hand.
First off, the series as a whole, in my opinion, is far and away the most well-crafted, passionate and best-written in the franchise. I love TOS, it's probably my favourite to just sit down and watch, TNG is just as great and probably has the highest amount of great standalone episodes of all the shows, but DS9 is unrivaled in terms of writing, story and characters. No doubt. The recurring characters on DS9 who we may only see a few times every season are more layered and complex than any of the characters in the other shows, it's incredible. The evolution and development they go through from the first episode to the final episode is shocking, it's unheard of in any other Trek before this. Just look at Nog. Not even a regular cast member and he goes from bratty little Ferengi kid who cares nothing for Federation rules, to young cadet with high aspirations, to Starfleet Lieutenant serving aboard the USS
Defiant.
The nine-chapter story arc to conclude the series is really just a gift to the fans who've been watching the show for its full seven-year run. It's everything you want or expect out of a DS9 finale and more. It's fully serialized and plays out like a good novel, it really feels like a work coming from the heart made by people who loved their show. And I loved it as a viewer.
What You Leave Behind is the final entry to this long story arc and an epic finale. The Federation have won the war, the Dominion have gone home to the Gamma Quadrant, Weyoun is dead, Damar dies saving his people but succeeds in driving the Dominion off of his home planet, Worf goes back to Qo'noS and takes his place as Federation Ambassador alongside Chancellor Martok, Miles ventures back home to Earth with his family, Odo goes back home to the Great Link, finally, back where he belongs... and Sisko, no, The Sisko completes his final trial and finds his place in the Celestial Temple with the rest of the Prophets. All that is left of the main cast on DS9 is Kira, Bashir, Ezri, Jake and Quark.
It's bittersweet, I may have never been as sad and as glad at the same time as I was. Sad, on the one hand, because I'll never see these characters again, but immensely glad, on the other hand, because they did it so well and tied up most of the loose ends. The goodbyes are incredibly tasteful and satisfying. I'm disappointed Jadzia was left out of the flashbacks, but that's understandable. It doesn't really matter, because all in all, they left it off in a perfect way. I swear, I don't ever get emotional with TV/films, never, but Miles hugging Bashir before leaving had me on the verge of bawling. That relationship and the relationships of all the characters make you feel at home on DS9, so seeing their goodbyes was quite sad, but very comforting at the same time. The final scene with Jake staring wistfully into space at the wormhole was real touching. His relationship with his father was one unlike anything I'd ever seen in any show, and that ending really does bring it all together.
This may be the last time we're all together. But no matter what the future holds, no matter how far we travel, a part of us - a very important part - will always remain here, on Deep Space Nine.
No better way to put it, Captain. Thanks for all the good times, DS9, you did yourself proud