Worf joining Deep Space Nine was a stroke of genius, in my opinion. It was logical he would be there, at least at first. The motif of Deep Space Nine is about oppression. Deciding to bring Worf onto the show did a lot for the Klingons. Without the idea of bringing him, we would've had a clunky way of getting the bad guys (from day one) in the Cardassians, to join forces with the Dominion. The Klingons killed and oppressed the Cardassians right into the Dominion's waiting hands. It is exactly
how the Klingons would respond to fear of an attack. Without that foothold in the Alpha Quadrant, it's doubtful Deep Space Nine has a reason to go to war. I mean, look at what they did before we went to war:
-- Destroyed the USS Odyssey
-- Destroyed New Bajor
-- Tried to start a war with the Tzenkethi.
-- Killed 29 people at a Federation Conference on Earth.
-- Tried to start a war between the Klingons and Federation.
-- Tried to get Gowron Assassinated.
-- Took Federation citizens hostage and replaced them with Changelings.
I mean, after all of that, what would it take to start a war? How about a bloodless take-over of the Alpha Quadrant where the Federation is fighting the rest of the territories against the Dominion? War was inevitable, but the Dominion started with the Cardassians, proved themselves worthy as partners, and then got other races to sign a non-aggression pact.
Without the idea to bring Worf on the station, how do we get the war? It would seem cheap and it wouldn't have served the themes of the show.
That's reason 1. The second, was it gave the Klingons a more honorable and complex society in DS9. Before Worf, there was the Klingon restaurant and Blood Oath
. After Worf, we had his brother, Martok, his son, the relationship with Jadzia, etc. He improved the quality of the show by making them more than just head-butting buffoons.
Reason 3: I enjoyed watching him turn from a Klingon, insecure as ever ("Do you hear the cry of the warrior?" "A demonstration can be arranged!" Every time a ship uncloaks, how tiring), to a man who embraces his differences, embraces that he is not Klingon or Human, but a mixture of both and he can set his own path. A man at peace that he never was on TNG. On TNG, his big role in the ensemble was to say "Captain, we should attack first, it's too risky to try diplomacy (I'm paraphrasing)." Here, he was in command, he had missions that were imperfect that he went on, and he became a more fully realized individual. They used Worf to make the show better. That's not like the Borg on Voyager where they didn't grow the Borg at all. It wasn't Q on Voyager where he just says "Kathy!" and not "Jean-Luc!"
They actually used him to make the show better. I can't imagine DS9 without him.