When this episode comes up in discussions it is often pointed out that it sets the show apart from TNG because Kira actually killed a guy.
That's odd because it's not the focus of the episode (which is Kira deceiving Odo, not Kira killing the guy).
Overall, I think you're underrating this episode quite a bit. The monologues might over-emphasize the noir mood to a degree, but they're also frequently hilarious (for example Odo's comment about humanity's urge to store records of everything).
Beyond that, this episode introduced Terok Nor and thereby added a whole extra dimension to the show that had been missing previously and would be exploited on numerous occasions in the future, either directly or indirectly (for example, at the end of Call to Arms
). When an episode makes an important contribution to the overall fabric of the series like that, while being awesome in its own right, that's about as much as a single episode can really accomplish.
For example, The Jem'hadar
makes a big contribution to the series, but as an episode, it's not on the same level.