A follow-up to two earlier episodes, "The Emissary" and "Sins of the Father", "Reunion" ties together two major threads in Worf's arc on TNG. The first time I saw it, I thought it was great; in retrospect, the episode has both strengths and weaknesses.
The strengths are obvious – Klingon's politics and Worf's attempts to fit in with his people. Robert Reilly, in his first appearance as Gowron, takes the creepy bug-eyed Klingon role and runs with it. Gowron was among the first DS9-ish characters on the show – not quite a bad guy, not quite a good guy.
The climax of the episode, culminating in Duras's spectacular death, is also worth mentioning as a plus.
The weaknesses are similar to those of "The Emissary". Lots of melodramatic talk here between Worf and his lover, but since we don't see her on the show much, we don't really care. Or at least I don't.
This episode is also noteworthy as the first appearance of Worf's son, Alexander. Most future episodes to feature him would be mediocre at best.