A couple of developments and one key scene make this episode more memorable than it really is. The first thing you should know is that "Menage a Troi" is a Lwaxana Troi episode, and it's also a Riker/Deanna Troi episode, and it's also a Ferengi episode, and it's also a Wesley Crusher episode...And despite all that, the best scene involves...Picard.
First things first. Lwaxana Troi was a signature recurring character for Next Generation (one of her later Deep Space Nine appearances actually references this episode directly), and this is probably the only time she is directly tied into the main events without having orchestrated them herself. Even still, it's not one of her better showings. It's not as clear when she's hanging out with her daughter why she's such a fun character to have around. That's why the Picard scene is so memorable (but we'll get to that).
Riker and Troi have a fabled romantic background that was sparingly touched upon in the series (though it finally led to a wedding in Nemesis), and while this is the rare episode to tackle it, it's also not an especially memorable instance, because it's mostly the same kind of window dressing character work featured in "Tin Man" a few episodes earlier. Alas.
Then there's the matter of Wesley. His status as a Starfleet Academy candidate was so screwy. You can't present him as a prodigy and then have him have so much difficulty getting into the program (as shown in the first season). Clearly all this backpedaling on his career progress was meant to simply keep him around, which was all well and good, although his character became more and more pointless the more he was used simply as just another character on the bridge. Seriously, this is the closest he comes all season to having his own episode. Because of yet another bogus excuse as to why he hasn't left yet, Picard decides to give him a field promotion to ensign. This was a far bigger to-do behind the scenes, where Colin Powell was present for a ceremony that saw Gene Roddenberry present Wil Wheaton with the second lieutenant bars from his very real military days.
Then there's the fact that this is a Ferengi episode. One of the most impossible tasks of the miraculous third season was rehabilitating the Ferengi, who were supposed to be one of the signature creations of the new series, on par with Romulans and Klingons, but whose first season appearances made them out to be more or less complete jokes. While "Menage a Troi" doesn't quite accomplish the task any better than the earlier "The Price," it's an important step in the direction of DS9, which is still the best argument for Ferengi redemption (though many fans still dispute that).
And then there's The Scene. In order to get Lwaxana out of the clutches of a would-be Ferengi suitor, Picard must convince him of his own genuine love for her. As anyone who has seen previous Lwaxana appearances knows, Picard loathes Lwaxana. He most certainly does not love her. And so this is a tall order indeed. He ends up using cultural differences to perform this trick. He quotes Shakespeare. Anyone who knows the Picard character knows he loves his Shakespeare. (He certainly loves Shakespeare more than Lwaxana!) And the fact that Patrick Stewart is the epitome of classically trained actors in Star Trek, any excuse to let him present such material will always be worth whatever the material provides. And yet it works so perfectly. The audience is aware of all the ironies, which are entirely lost on the Ferengi. It works. Lwaxana is saved. And Picard gets the best scene in an episode that otherwise really has nothing to do with him.
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Memory Alpha summary