Alas, Poor Scrappy: The viewers' dominant reaction to Elizabeth's death and George's grief over her.
Angst? What Angst?: One would expect that Dwight's PTSD would be a major challenge for him and Caroline, but one conversation with Hugh Armitage appears to cure him and the arc is completely abandoned. Repeated in season 4, when instead of dealing with their shared grief over the death of their daughter and Caroline's flight to London the story has them simply move on with life as if the giant angsty elephant in the room doesn't exist.
Arc Fatigue: Drake and Morwenna pine for each other after her marriage for some of series 3 and all of series 4. They Do get their happy ending in the series 4 finale, but the happiness is one scene compared to a whole season of sad pining.
Base-Breaking Character: Francis. He's either the series's biggest woobie or an annoying whiner who drags everyone around him down with his continued stupid decisions.
Complete Monster: Reverend Osborne "Ossie" Whitworth is secretly a lecherous creature who will stop at nothing to satisfy his urgings. Teaming up with George Warleggan to coerce Morwenna Chynoweth into marrying him to spite Drake in lieu of hanging him, he wastes no time getting it on with her in brutal fashion. Eventually, they have a child, John Conan, but he continues to rape her despite Dr. Enys warning him it could kill her eventually, proving to be a hypocrite when the next season he claims to be concerned about John Conan's life. Deprived for a while of satisfaction from Morwenna, Reverend Whitworth bides his time by pursuing an adulterous affair with her sister, Rowella, and helping George bankrupt Pascoe, one of the few remaining moral bankers in Cornwall, by extracting a confession of embezzlement from Pascoe's dying partner, Nathaniel Pearce, and casually cursing both Rowella and Nat the instant their usefulness ends, and is all too ready to resume his abuse of Morwenna at full force.
Creator's Pet: Debbie Horsfield has admitted Drake and Morwenna are two of her favourite characters which many fans felt was the reason they got more screentime in season 3 than their plot warranted.
Reverend Whitworth, already a despicable pig, crosses it by raping Morwenna almost immediately after his child is born, if earlier piggish moments towards her hadn't already done it.
When George has Tom Harry blow up Drake's workshop over Whitworth's grisly death against Elizabeth's clear wishes, it's clear they're both over the MEH and that George is the only major character to survive Series 4 who won't get a happy ending at the end of the season.
If Monk Adderly didn't cross it by making unwanted advances on Demelza in Ross's own house, he does so by refusing to consider the matter between him and Ross to be settled when neither is wounded during the duel, resulting in Ross killing him.
Romantic Plot Tumor: Dwight/Caroline in series 2 for some, Drake/Morwenna in series 3 and 4 for others.
Seasonal Rot: Season 3 and 4 are commonly argued to be of poorer quality compared to the first two seasons.
Squick: Whitworth sucking a prostitute's toes and heartily enjoying it.
Again, Sam's relationship with Emma Tregirls was cut down to a minimum.
Dwight's imprisonment and separation from Caroline could have been milked for drama but ended up taking the backseat to other plots.
Values Dissonance: In the source material, published in the 1950s, it is clear that Ross rapes Elizabeth. Despite efforts to update the scene for a modern audience and portray the sex as consensual in the TV adaption, many viewers still felt uncomfortable with what they considered dubious consent at best.
Most gowns featured in the show are hopelessly old-fashioned for the 1790s, until everyone starts wearing classic Regency costumes from one moment to the next, without showing the transition in fashion that took place during the time.
A lot of Demelza, Elizabeth and Morwenna's maternity gowns are laced quite bizarrely, and in some cases it's painfully obvious that their pregnancies are fake since a) no one seemed to take into account that pregnancy often causes women's breasts to increase in size and b) the fake stomachs are positioned far too low down on their abdomens. The result is that it seems as if their stays are actually trying to squeeze their babies out of them, like a tube of toothpaste!