The show finally realises that Worf is a member of the cast, and gives him a meaty story of his own. It's great that they elected to continue a story thread back from TNG and we get to see Duras again, although the change of actor makes him nothing like the weak and whiny little boy he was before and hard to reconcile.
Part of the joy of this episode comes from having John Colicos back as Kor, and the interaction he gets to have with Michael Dorn is wonderful. Both of them absolutely bring their A-game in a story in which the lure of power begins to corrupt them. Dax is unfortunately stuck in the middle, and it's easy to understand her exasperation. Worf begins to act like a bit of a maniac and certainly differently from what we're used to, but it shows how much his Klingon heritage really means to him.
I like the extreme ends of the spectrum in which both Kor and Worf display what it means to be Klingon. Kor is always jovial, loud, boisterous and ready to jump in, while Worf is stoic and centred, rarely smiling. They both embody the traits that you would expect of "pure" Klingon and yet both are opposites of each other.
It's a shame that so much of the episode is spent wandering around boring caves, and that the end leaves things kind of abandoned.
I would have liked it a lot better if the sword would have had some kind of meaningful impact on future episodes. It was a pretty big letdown that they decided to end it the way they did. And I didn't care much for the bickering between the Klingons over the sword.
I would have liked it more if the sword or the caves were messing with their minds in some artificial way. Kor going mental I would maybe understand, but Worf suddenly lusting for power, that didn't sit well with me at all.