The first regular episode following the pilot is underwhelming, but still solid. I assume they blew most of their budget on the premiere, so had to stick to smaller stories for a while, but DS9 was always a show about the characters and it's not at all out of place that we dive into what makes these people tick.
The introduction of Garak, the Cardassian tailor/spy, is the big draw here. His first appearance isn't anything special, but Andrew Robinson brings charm to role and distinguishes himself clearly from other Cardassians. He's polite, happy and thoughtful - which in some ways makes him even more menacing. His description of himself as "plain, simple Garak" tells us that he's anything but. Right now we don't really understand why he's on DS9 or what his background is, and the show will continue to play with our expectations of him. It's also hard to believe that Dr. Bashir is so dense as to not understand what Garak is trying to tell him.
The episode is a good showcase for Major Kira as she has to fight against the person she's been all her life. The problem is, at this point we don't know who Kira was before, and her dilemma doesn't strike any chord.. It's easier to get a grip on things after knowing her character through watching the show previously, but for a new viewer I can imagine it's hard to care. For all that, Nana Visitor puts in a heartfelt performance and it's very clear that she cares. I like her conversation with Odo and the fact that he just makes a decision based on it. A lot of the details about her history with Tahna Los and the Kohn-Ma terrorist cell are provided in the Terok Nor novels, but of course they're not canon (however well they manage to fit in).
The Duras sisters were a fun addition, keeping the links to the TNG universe alive. It's also impressive that even this early, the writing is so much more mature than on that show.