"Vortex" is an episode that would have far greater importance if the series had not last so many seasons. It's one of the few entries where Odo, theoretically on a quest during the first two seasons to discover his origins, thinks he makes some progress. Of course, at the start of the third season, he finds out who his people are, and his journey is forever altered toward a more direct conflict with them, one of the few instances in Star Trek history where a central character rejects and is rejected by their own kind (even Worf had a love-hate relationship with his fellow Klingons, and Seven continued to be fascinated by the Borg even after acknowledging that they nearly wrecked her life).
Much of the plotting in "Vortex" is hopelessly convoluted, but a stranger who possibly has the answers Odo seeks leads him to interesting conclusions, and in a very roundabout way might even be said to be vindicated once the truth about his origins is revealed.
It's a fine episode to watch in its own right, and continues the trend of the odd shapeshifting constable Odo making for compelling television.
franchise * series * essential * character
Memory Alpha summary.