TNG - Symbiosis. Yes, the story has some good themes. Yes, as a microcosm the episode just about works. On any practical level? No, it's fundamentally flawed. Even for sci-fi, this story is making things waaaaaay too narrow and parochial in scope for the sake of the plot. The plant can only grow on one planet. Nowhere else? Not even via controlled, hydroponic greenhouses? Granted, the dialogue almost manages to sell the idea of the one planet selling the dope to the other that's doing all the work for them, on top of getting high - especially with the Ornarans not knowing how to fix their shuttles... really, nothing else grows on Brekka except the drug plant? No industries where they can build their own ships?! Amazing they didn't take notes while the doped-up Ornarans were getting the latest crop. And Ornara has everything else, including working comm systems, and nobody there knows how to maintain diddlysquishles?
For my part, I feel like "Symbiosis" had some good potential but the execution is pretty terrible. It seems way too simplistic for the Brekkians to literally have only a single industry (felicium) and not other essentials, even if they get a lot of benefits from the one-sided trade with the Onarans.
It's also a prime example (for me anyway) of what's wrong with early TNG Prime Directive episodes. Picard ultimately decides not to give repair parts for the ships, knowing that stopping the drug trade will have a severe impact on both worlds, yet earlier he flat out rejects Crusher's offer to make non-addictive felicium on the grounds that it's too much interference? How is choosing to wash their proverbial hands of at least one side losing spacefaring ships (as well as being addicted to a narcotic) not considered both interference on a higher scale and interference that's more potentially destructive? There's a lot of consequences that the script simply glosses over.
Diddlysquishles is now my favorite word.
For my part, I think TNG's "Justice" is a good example of a plot that fails on many levels. The final version is kind of like an update on "The Apple" but the Edosians come across looking much sillier and there's no logical reason for having a death penalty for justice, not least over trivial things like Wesley falling into a garden. And even less so for visitors.
It would have been far more interesting if the earlier drafts by John D.F. Black (who was credited with pseudonym Ralph Willis in the final version, because of how much the script had drifted from his original concept) had been worked on, IMO.
In an earlier version, the setting would have been a more dystopian world (Llarof) that had been wracked by chaos and violence, and the "death penalty for everything" policy was created to finally instill a measure of order. It was successful, but the governments that followed have become a bit too reliant on its enforcement. Picard would have become involved when one of the security personnel is accidentally killed, and he learns that a rebel faction is seeking to overthrow the existing regime.
In one draft, they would have succeeded but then kept the death penalty as a form of justice (as well as power), and the central question would be whether having such power can ever be used to create real peace and justice, or whether it's mainly just a trap.