For more than three years, TNG tried to develop a hostile alien race that could occupy the same space in the firmament as Klingons and Romulans. Everything they tried until this episode failed. (The Borg could never be a regular threat; they were only good for one episode a season.) Cardassians hit the right note, and this episode became the inspiration for DS9 and ultimately VOY. Pretty good impact for an episode where none of the three leading characters (O’Brien, Capt. Maxwell, Gul Macet) are regulars: the only Picard himself plays is to coax O’Brien, question Maxwell, and chastise Macet.
And this scene is one of the best in the franchise’s history:
The episode's only flaw the title: should have (obviously) been called "The Minstrel Boy."