I would have to say yes.
Other shows have awesome plots, well choreographed fights,...but even the best script won't survive if people don't love the characters involved. It doesn't matter whether they love them or love to hate them.
DS9 felt like a community, which is more then the enterprises and voyager ever did. Both the good and the bad things associated with it.
It wasn't just a stellar main cast...which they had. It was the many other characters that they just kept building on.
Sisko is my default star fleet captain for both character development and sheer awesomeness. He was tough as nails, but also funny, had a strong family and always sincere. He wasn't the first regular black starfleet captain to me...he was the starfleet captain that all others would be measured.
Kira I loved as 2nd in command and while she calmed down over the years, she was a tough old gal who was essentially rediscovering her Humanity (or her Bajority) in the process. The love story was just icing on the cake.
Odo would have been a one maybe two parter at most. Instead we got to see him develop over a 7 year period and found out stuff that both blessed and damned him.
Worf is probably the best character to compare the differences between tng and ds9. On tng he was the guy they beat up to show how tough he is. Near the end of the series they were trying to show off his kung fu action but it was almost a sideline. Hell the most memorable scene of showing off his awesome skills wasn't the series, but first contact, when he pulls out a blade and shows off his stuff against the borg drone. and even then he wasn't the savior, merely the tough guy. The savior role was reserved for Picard, Riker and Data more or less only.
In DS9 Worf had to abandon the culture he dedicated his values to in the very first episode. He was put through the ringer at a deeper and more scathin level then anything that happened in tng...and that was just in the first episode. Worf was shown to be extremely skilled, tough resourceful and often had the answer when nobody else did (his use of tractor beams showed he wasn't just physically tough, he was canny as well). He had to say goodbye to his brother to keep him alive, made amends with his son who was, let's be honest a joke character that actually got better when he become an adult, got married and lost her, and above all else, was considered the warrior of the group. He butted heads with Odo with security and was often right. Finally he regained his honor and his house and made friends with a man who you thought was the enemy of everything Worf stood for.
He was a truely 3 dimensional character that was allowed to shine.
Miles O' Brien has a similar story. In TNG he was a one note character and didn't even have Worf's regular billing. While he kinda got an episode or two, most of the time he was a "recyclable red shirt". Once he got on ds9, he was a family man, a darn good tech, a bit of a bigot that learned from it, a great holodeck buddy, a pub man, and an ex soldier. He might not have the miracle worker status of Scotty, or the interesting skill set of Georgi la Forge, but you knew when he set stuff up, it meant business. Plus his humor really added to any scene he was in.
The Dax entity's and their hosts was a great idea that added to the environment to remind people, this just wasn't the yanks in space. In many ways I'm glad their was a transition, but it should have happened half way through the series. both hosts were different . Jadzia was a warrior woman at heart with a lot of science under her belt. Ezeri reminded me of your pet puppy in manner and disposition.
If I had to say the most improved character in the series, it was Doctor Jullian Bashir. He starts as a brilliant newb who is pretty much the most hated member of the main cast. But through character development and interaction with many awesome characters, he begins to grow up and becomes a really amazing character. His genetic engineered nature only added a new facet to explore stories.
Quark was what happens when you subvert the concept of Guinen and play it in a more realistic manner. Unlike the majority of the characters above, Quark didn't go through much character development, but as a plot device and a character, he was brilliant, especially in showing Ferengi's culture and physiology. He was lovable, in spite of his nature.
If their is one place that DS9 shined when it came to character development, it was it's use of children. Jake and Nog started off as relatively realistic kids and we got to watch them grow up. While Jake suffered from "wonderboy" syndrome to begin with, as he got older, he broke many of the common conventions that make star trek kids bloody annoying. While they kinda wrote him into a corner, he did well. Nog on the other hand went from whiny brat to one of the best junior officers in the fleet. He was a neat blend of both his cultural values and star fleets military tradition.
This is why I love ds9.
In another series, he would have been a 2 parter and then discarded or devolved into an extra.
Instead, in many ways this is the day Nog became a great unofficial main character, up there with Garek.
Hell to this day, one of my most favorite scenes is when Jake and Nog share an apartment and it's Nog whose the straight laced one.
and it shows something that is often swept under the carpet despite being one of the Ferrengi's best traits: they have one hell of a work ethic.
Villains were solid in this series. The Cardassians were a brilliantly talkative people that had just raped a planet. They had one of the best spy agencies in the entire alpha quadrant and were alien in both feel and design, while still feeling sympathetic in some ways.
Gul Dukat was an amazing character ride that truly earned a place in the top 3 trek villians. While I didn't like the last couple of year turn, it kinda made sense and really should have been the base for the ds9 movie. Damar went from flunky, to great leader, to martyr all while showing his qualities of whom he is. His last season development should be a case study on how to build a character quickly, while not taking time away from the rest of the main cast.
The Dominion is an amazing villain that is uniquely suited to the ds9 environment. On a spaceship, a shapeshifter is comparatively easy to track down. On a station with people coming and going, it can be a needle in a haystack.
Then you mix in their servator races: the Jemhidar and the Vorta and you feel like that when they looked through the wormhole, the wormhole starred back. Hell Weyoun you got the feeling that if he weren't a middle management slave he'd be almost likeable.
The Klingon empire roared during ds9 and it added both worthy adversaries and loyal allies. Martok is an amazing character in his own right and if they would have done a star trek: birds of prey he should have been a reoccuring character.
However, the most hated villain isn't Dukat and the Cardassians, or the Dominion or the Klingons...it was a single elderly bajoran trying to gain ultimate power. Wynn was the character you absolutely loved to hate, especially when she was right. She pushed her beliefs and her needs to the point where you really wanted to see her fall.
But it wasn't the heroes and villans that made this show something special. It was the many different characters that would have been redshirts on any other shot. From Morn...who didn't even need to talk, to Rhom...an excellent example of what happens to Ferengi who don't have business savvy, to his wife, a Bajorian bimbo who, when coupled with Rhom, added a whole new dimension to both.
and above all else, I learned what a simple tailor can do