This show is, in many ways, the anti-Trek: it takes place on a space station! They're not even trekking! They are chilling out next to a friggin' wormhole with aliens who have incredible powers and no sense of linear time and a planet with people who worship said aliens, believing them to be their Prophets. That planet is none other than Bajor, first introduced in TNG, now free from the Cardassian Occupation (the first few seasons of DS9 run concurrently with the last few seasons of TNG, so I did come into the show with one spoiler for a plot point that was supposed to be initially introduced on this show). DS9 brings over the Bajorans, the Cardassians, the Ferengi, even the Trill—all alien races from TNG characterized by the classic Trek motto "One Race, One Character Trait"—along with old favorites like the Klingons and Romulans...and deepens them all as it examines what it is actually like for the Federation to share space with these other aliens. The DS9 motto seems to be "Thanks for all these toys, TNG, now we're going to break them!"
Deep Space Nine, unlike the Enterprise, feels like a real place where people other than the main characters live, people who can be affected by the consequences of Our Heroes' actions. We see so many different areas of the space station rather than spending most of our time on the bridge. And who are Our Heroes? Benjamin Sisko, who's almost as unlike Picard as Picard is unlike Kirk. He's proud, fierce, and righteous, but he's a bit more flexible morally and ethically: he's a realist, not an idealist. And he's a father! His son, Jake, grows up over the course of the series, and Sisko's relationship with Jake is one of the show's strong points; it's far better than the one between Beverly Crusher and Wesley Crusher, which...barely existed. Kira Nerys, a former Bajoran freedom fighter (or terrorist, depending on who you ask) who serves as the liaison between Starfleet and Bajor (this character was supposed to be Ensign Ro, and in the early episodes, I imagined a show with Ro, but Kira becomes a wonderful character of her own, with a troubled past and also some flexible morals). Jadzia Dax, a female Trill science officer who knew Sisko when she was the male Kurzon Dax, whom Sisko affectionately referred to as "Old Man." I love the relationship between Sisko and Dax a lot because they have so much more history than anyone else on the station. Julian Bashir, charming genius medical officer with the utmost concern for his patients, whoever (or whatever) they may be. Miles O'Brien, Everyman engineer with a wife and kid. Odo, shapeshifting security chief with a mysterious past. Quark, Ferengi bar owner with the utmost respect for the ways of Ferenginar. I mean. Just look at that fucking character list. Realize I haven't even mentioned awesome supporting characters like Quark's brother and nephew, Rom and Nog, and Garak, the only Cardassian on DS9, a plain and simple tailor. AND DON'T FORGET PERPETUAL BARFLY MORN. Put all these incredibly different characters on a goddamn space station and just watch what happens.
As with previous Treks, I watched an abridged version, but this was the least abridged of the three series, as I ended up watching more than 75% of the episodes. The biggest cuts were in the first season, understandably, as the show was still figuring itself out, but once it started introducing serialized storylines, it really took off. I wasn't sure how the storytelling would work in a static environment, but they made it work. Since they weren't on a starship that could go out and find trouble, trouble often came to them! And they could also take smaller ships out exploring (often through that friggin' wormhole) and discover a whole host of trouble. I don't even want to say anything about the host of stories because they came as a surprise to me, but as a rule some of the most successful stories involved the Cardassians—who are trying to deal with losing control of Bajor just as the Bajorans are trying to deal with interacting with their former oppressors in any civil way—and some of the least successful stories involved the Prophets—who basically make no sense and speak in riddles and can do anything the plot requires them to. That being said, this is the best depiction of religion I've seen in science fiction since...well...Battlestar Galactica. It is a show that respects that people have beliefs, and that their beliefs are important to them, even if others don't believe the same thing.
Star Trek: Deep Space Nine is an amazing show that was ahead of its time. This is what we want from our television today, and it was doing it in the nineties. A diverse ensemble cast, with characters getting spotlight episodes, even ones not in the main cast. Long-term arcs full of surprises and emotional payoffs. A charismatic villain who has one of the best character arcs in the series. Complexity and moral greyness up the wazoo. This is top-notch science fiction right here.