These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Abandon Shipping: Interest in Arthur/Morgana had already begun to wane after their dramatic decrease in scenes together during series two, but the third series revelation that they were secret half-siblings ended it for a lot of viewers - though there are still some fans out there.
On a similar note, another Accidental Aesop that can be drawn from the finale is: "if you sit around and just wait for destiny to happen, it'll never actually happen."
Accidental Innuendo: - without a doubt. The frankly ridiculous levels of Ho Yay between Arthur and Merlin make this trope unavoidable anyway, but then we have the sleeptalking sequence…
Merlin: Go on Arthur...faster...move it...climb!
One can only imagine the faces of the guards outside Arthur's room listening to this exchange. Merlin was holding onto a rope that allowed Arthur to escape from his room. Unfortunately, the rope wasn't long enough and Merlin was forced to drop Arthur halfway down.
Arthur: (muffled) What are you doing...the rope!
Merlin: panicking) THERE IS NO MORE ROPE!
Arthur: (straining) Merlin...
Merlin: (groaning) Oh...I don't know if I can hold on any longer!
Arthur: (even more strained) ...don't let go of the rope!
(Merlin groans until there's a startled shout and then a thump)
Not just Arthur and Merlin.
Lancelot: Do you submit, Sire?
(Guards restrain Lancelot. Arthur gets up, apparently angry, and grabs his sword.)
Arthur: On your knees.
Also quite prominent in the season 3 premiere, with Arthur's quip of "aww is your little bottom sore?" after Merlin complains he's been in the saddle too long.
Happens so frequently that even the actors aren't impervious. During Comic Con 2011 Bradley James kept discussing how he liked to get his sword out and wave it around. Either side of him, Anthony Head and Katie McGrath try to stifle their giggles.
Actor Shipping: Bradley James gets shipped with all three of his co-stars, especially Colin Morgan. Colin/Bradley's fanbase is almost as big as the Merlin/Arthur one. Also, Colin gets shipped with Katie McGrath (Morgana) quite often, as well.
Angel Coulby and Rupert Young, given the two seem to be quite chummy on-set, do a lot of promotional work together, and have been paired up for at least one DVD Commentary.
The Guards of Camelot often appear so utterly useless. Its gotten the point where its gone beyond simple passive aggression to looking like they actively let the villains of the week in because they're hoping Uther will be killed.
Arthur, at least in regards to how he treats Merlin. A lot of fans think that either he already knows Merlin is a warlock, or he at suspects that he is and is in denial. On the other hand, there's the question of whether he really deserves to be king, as he needed help to draw the sword from the stone, has been easily manipulated throughout his entire kingship, and doesn't seem to realize that a crisis is the worst time to go into Heroic BSOD.
Gwen following the events of The Dark Tower. Did Morgana finally get sick of her resisting and outright enslave her mind, as most people suspect from the final scene between the two in the tower? Or did the mandrakes leave her so open to suggestion that she just went along with whatever Morgana said? Very few people believe she turned of her own free will, and a few even theorize that she's pretending to have turned to get in good with Morgana. Really, Gwen at this point is very open to interpretation.
Finally answered in With All My Heart. Gwen's spirit was pulled out and replaced with Morgana's will.
As of the finale, there are several "Kilgharrah was a giant troll" theories floating about.
Angst? What Angst?: All those evil deeds Gwen did while brainwashed, i.e. murdering an innocent man, poisoning her husband, sending several men to their deaths seem to have zero effect on her in the episodes after. What, did they just not tell her what she'd done?
Arthur has been betrayed by every single important person in his life: Uther, Morgana, Agravaine, Guinevere, Lancelot note though Lance/Gwen were under a spell when they betrayed Arthur, no one ever finds out about it, Mordred and even Merlin and Gaius by keeping the truth about Merlin's magic hidden from him for so long. You'd think this would have some sort of long-term psychological effect on Arthur's ability to trust people, but after a brief period of unhappiness he always bounces back.
Arc Fatigue: Most would agree that the withholding of Merlin's magical reveal has gone on way too long. It finally gets resolved in the series finale after Arthur is mortally wounded and his canon fate all but assured.
Arthur becoming king was another one. It's resolved, but in a way that will further the above Arc Fatigue. Uggggggh.
Badass Decay: Let's face it, on a show where Status Quo Is God, the character of Morgause was simply too intelligent to avoid getting this treatment for the storylines that the writers wanted. In her debut episode she storms into Camelot, single-handedly takes down several guards, challenges Prince Arthur to a duel, beats him, drops a bombshell about his mother, makes him chase her across the countryside for answers, shows him what may or may not be a real apparition of his mother who tells him that his father was reponsible for her death, and then watches from a crystal as he goes storming back to Camelot to kill King Uther in a fit of rage. Fast forward to season three and she's a completely ineffectual and one-dimensional villain who plots to overthrow the kingdom with a range of increasingly convoluted plans. She still gets the occasional Bad Ass moments (the pillar of fire), but her IQ has dropped exponentially and she's eventually taken out by Gaius. Gaius. How embarrassing.
Mordred in season 5, at least in regards to magic. He's a still a badass knight, but he's quit using his considerably powerful magic. It's justified in that in the years between his last appearance in season 2 he's been hiding it, and has got used to life without it.
To a much lesser extent, Alvarr. Some found him if not entirely sympathetic, then at least an interesting and charismatic Well-Intentioned Extremist, with intriguing ties to Mordred, Morgana and the Druids. Others just found him manipulative and skeevy.
And now Agravaine, for much the same reasons as Alvarr. For some he's an enigmatic wild-card with yet-to-be-revealed motivation, others find his lecherous behaviour around Guinevere and Morgana extremely creepy and disturbing.
It seems that Mordred is getting some of this in season 5. On one side, you have the fans who absolutely adore him and wish that he wasn't Doomed by Canon. On the other, you have the fans who wish that he had died in "The Disir".
Broken Base: The finale. Some found it satisfying, others criticized the dangling plot threads, i.e. Aithusa, what happened to the kingdom after Arthur died.
It gets worse due to the magic ban only implied to have been lifted rather than explicitly shown. Gwen knows about Merlin and respects what he did, so while she didn't have the authority at the time, it's heavily implied that she did lift the ban. And yet the fact that there was no real closure is more than enough to cause this.
Cargo Ship: You'd be surprised at the amount of fans who have taken to shipping Arthur/Merlin/Hat.
Crazy Awesome: Dragoon. Merlin has to avoid snarking at important people, act like he's helpless, and maintain some level of sanity so no one suspects him. Dragoon, on the other hand, tears into King Uther for his crimes, hams it up like crazy, forces Prince Arthur to give him a piggy-back ride, and uses knights as steps to get on his horse when they annoy him.
The music played at Arthur's coronation is a more epic version of the credits music.
The soft piano played when Arthur sees Excalibur in the stone. Just a single muted piano with a soft background, and the impression that no one is there but Arthur, Merlin, and the sword. Ends a couple seconds later, but it's awesome in its simplicity.
The gloriously creepy refrain in The Tears of Uther Pendragon when Merlin follows Morgana out into the forest. Coupled with the visuals (Morgause arriving in slow-motion on horseback, Morgana standing alone in the midst of the trees) it's a true spine-chilling moment.
Designated Villain: Morgana, Mordred, and Morgause (who doesn't really do anything particularly villainous, and some of her actions even heroic, like putting the entire city to sleep to assassinate Uther without actually killing any innocents).
In an interview near the end of series for, the show's creators had this to say about Aithusa:
There’s a surprising twist at the end of this series that becomes a big part of series five. It’s fair to say that a character we’ve met before returns, an evil character, and I think people can probably guess who that is.
So far Aithusa has done two, and only two things in the course of the show: a) hatch from an egg, and b) heal an injured woman. How this translates to "evil" has yet to be revealed.
Although, to be fair, the white dragon is the one character in the Arthurian legends and their adaptations that never gets portrayed sympathetically, and Word of God confirms Aithusa does have a Freudian Excuse rather than just being Always Chaotic Evil as in other adaptations.
Die for Our Ship: Guinevere and Lancelot get the worst of it, the former from Merthur and Armor shippers, and the latter from Arwen shippers.
Mithian was around one episode and is getting this from the Arwen shippers.
Nimueh: She was the breakout villian for the first season, and was popular enough that many fans hope that Morgana and Morgause would bring her back from the dead. Sadly it never came to pass
Sir Leon. He is literally too popular to die. Introduced at the start of season two, the fandom latched onto him as a recognisable Mauve Shirt among the Red Shirt Army of Camelot's knights. After his apparent death at the end of series two, his popularity among the fans and other actors on the show secured his Unexplained Recovery and a larger role in every series that followed. It all came to its natural culmination with this spoof interview in which actor Rupert Young explains why Leon is so integral to the show.
Aredian the Witchfinder. He was one of the few villians in the show that didn't use magic, and he had the added bonus of being played by Charles Dance.
After being Brainwashed into twisted versions of their true selves, Lancelot and Guinevere get a sudden increase in sex appeal.
Averted with Merlin, who is usually pretty sexy, but can only be described as pretentiously goofy in his evil state.
Well, "evil" is stretching it, but Mordred in series 5 has tons of fangirls.
Fan Nickname: The Slash Dragon, because the Great Dragon is always talking about how Arthur and Merlin are meant to be together.
Merlin and Gwen are often called the Camelot Detective Agency. And with series 3, Morgana became Smirkgana.
Agravaine was already being called Uncle Creeper after his first two appearances. Once he hit Scrappy status he became known as "Aggravating".
"Agrapain" is also quite popular.
Fan-Preferred Couple: Arthur/Merlin and how. Many fans watch the show just to see them together. On every youtube video that the two appear together in, almost all the comments are about the homoerotic subtext in their relationship, about how good they look as a couple or how they are secretly boyfriends/married. Not to mention that there's another fanbase almost as large as the Arthur/Merlin one, just for Colin Morgan/Bradley James.
Foe Yay: Merlin/Nimueh and perhaps a hint of Uther/Nimueh. The theory that they have a child together was Jossed in Excalibur, which is conversely the episode in which they seem the closest.
In series three Merlin and Morgana crank this Up to Eleven, what with all the sweaty sword-fighting, smouldering glances, dragging each other into alcoves, and the fact that they're spending almost every minute obsessing over each other.
Arthur/Morgause. After the events of Sins of the Father, Arthur sees red every time they cross paths.
Inevitably Gwen/Morgana after spending the first two seasons as a Romantic Two-Girl Friendship. During the course of season three, as Morgana begins to realize that Arthur and Gwen are an item, several scenes can be construed as Morgana getting jealous, or of her trying to seduce information out of Gwen, what with all the hand-holding and fake hugs.
Agravaine and Guinevere. It's mostly one-sided, but Agravaine is acutely aware of Gwen's presence, is deeply interested in her relationship with Arthur, refers to her as a "beautiful woman", has tried to touch her hair without her noticing at least once, and seemed rather intrigued with Morgana's claim that Guinevere would one day be Queen.
Morgana spent the end of 4x12 checking out Gwaine, although she was also mocking him and making him fight to the death at the time.
Merlin's rant in The Once and Future Queen becomes this. It's pretty funny at the time, but then the second half of the series kicks in and he's permanently cemented himself as a The Woobie, and the fact that he could have an extensive rant about his normal life before all that happened just makes it all worse.
In the episode The Once and Future Queen, Guinevere asks Arthur: "would it kill you to say please and thank you once in a while?!" In in the series finale, Arthur's last words to Merlin are: "please hold me" and "thank you". So yeah...apparently it does kill him.
In "Queen of Hearts" Arthur and Guinevere eagerly look forward to the day that Arthur becomes king so that they can finally be together without fear of reprisals. Which means both are looking forward to the day Arthur's dad finally kicks the bucket.
In series 1, ep 2, the Dragon says of Arthur and Merlin: "The half cannot hate what makes it whole". Fast forward a couple of years, Inception comes and give us this line, from Mal: "Do you know what it's like to be a lover? To be the half of a whole?". Slash fans did not fail to pick up on this.
One of Bradley James's first roles on television was in the detective series Lewis in which he played the third point of a Love Triangle. Given his role in the famous Arthurian love triangle, it's rather amusing to see the actor playing the role of Lancelot elsewhere.
And then in the film Fast Girls, where once more he's in a Love Triangle...this time as the Guinevere!
In The Coming of Arthur Uther is dragged before the throne, de-crowned, and forced to bow before Morgause. After a few angry words, Morgana steps out from behind the throne and confronts him. Theatrically done, but it does make you wonder just how long she'd been hiding behind that throne waiting for the right time to make her grand appearance.
In the episode where Uther falls prey to a mandrake spell, he goes mad and tries to run to the frontline of an ongoing battle for Camelot, but Arthur manages to pull him back. Which should have settled that case... until Uther suddenly takes a completely out-of-nowhere arrow in the knee.
Ho Yay: Lots and lots of it and even to the point where many fans watch the show for the main reason that Colin Morgan (Merlin) and Bradley James (Arthur) look really good together. There's a main page of this.
Iron Woobie: Merlin. His normal life consists of having to save the day off-screen because he will most likely be killed for his efforts for no other reason than he's a warlock, something he can't control, is abused by Arthur despite constantly putting his life on the line to protect him, and is considered an idiot despite the fact that he's always right.Once in a while, something good will happen to him, such as finding his father, falling in love, and finally getting a chance to show Arthur magic will be good...no, it's Yank the Dog's Chain. Even so, he keeps pushing on, never even letting on how much he's hurting, taking comfort in that fact that there's one person in Camelot who knows how much he's done, and holding a firm belief that because Arthur is a good man, he will one day be able to see magic for what it is.
As of Season five, Morgana seems to be approaching this.
Mary Sue: Ability wise Merlin. He's immeasurably powerful without so much as Kryptonite, everyone who meets him immediately likes him and if they don't, they're automatically a villain and his eyes even change colour. He reaches his height of Mary Sue - dom in the final episode when it turns out that he is the personification of magic and the world. Though he doesn't fit the second half of this trope, as he has many character faults, which other characters are quite willing to point out, that ultimately get in the way of him achieving his goals.
Showing a picture of a couple prone to ship tease, followed by the ship from Peter Pan and the caption "this ship sails itself".
By it's prevalency in the fandom, you would think that the phrase "two sides of the same coin" is brought up so often on the show that it could count as Arc Words. In truth, it was only ever said twice, both times very early on in the show's run.
Memetic Sex God: Unlike nearly every other character on the show, Merlin rarely gives out Fanservice of any kind, limiting it to one Shirtless Scene in the pilot. However, this has just made the fandom turn everything into Fanservice, including his smile, voice, and forearms whenever he rolls up his sleeves. The scene in The Disir where he walks around in a nightshirt that does show off a small portion of his chest has been dubbed the "Almost Shirtless Scene".
Moral Event Horizon: Morgana spent from a year away from Camelot in the company of her half-sister and returned as The Mole, having performed a Face-Heel Turn in the interim. Over the course of the third season, her plots to bring down her father and half-brother have intensified in brutality, but it's not until Queen of Hearts that she crosses the line and ends up framing her servant and former best-friend Guinevere for witchcraft. Why? Because she had a dream that Gwen would one day become Queen of Camelot. Up until that point, fans were capable of some degree of sympathy for Morgana's Well-Intentioned Extremist views, but after seeing her smiling to herself as a terrified Gwen is hauled away to be burnt at the stake, the general consensus became: "the bitch must die!"
Uther from that same series passed the horizon before the series even started. He committed the "Great Purge" in which he hunted down and killed anyone with magical blood, even drowning children of magical parents in fear that they inherited magical blood. In series he wanted Mordred killed when he was still a child, and had his guards kill an unarmed man who escaped from his dungeons, even though he surrened
Most Wonderful Sound: Arthur pronounces Guinevere's name (with an emphasis on the vere) as though it's the most beautiful word he's ever heard. Even non-shippers have been known to admit that the way Bradley delivers those three syllables results in a few tingles.
Narm: Morgana's nightmare in The Darkest Hour would have been much more effective if it didn't include the Crowning Moment of Funny from Queen Of Hearts.
Also Morgana's "I WANT HIM (Arhur) DEAD!" line, screamed like a three year old having a tantrum
The Burger King crown.
Mithian's poor choice of simile when she recounts the massacre of her people: "They cut us down like... corn." Corn?
Gaius storms into Camelot in order to help Merlin defeat Morgause. Nothing wrong there, but the word that he yells in order to throw her across the room sounds like: "OATS!"
Gaius often reminds Merlin to keep his magic secret, at all costs. Too bad he usually either screams it or says it while standing right next to someone Merlin's supposed to hide his magic from. But if no one has noticed in 4 season and the 10 years taking place between seasons...
Nausea Fuel: Try watching the Lady Catrina eat her preferred type of food and not feel like barfing...
Newer Than They Think: Arthur was shown lighting candles with matches in "The Darkest Hour". Even though matches are Newer Than They Think, having been invented in 1826, most would know that there were no matches a whole millenium before firearms. Even the predecessor to the match (invented in China in 577 AD) had yet to be thought of. More accurately in those days, flint and steel would have been used to start fires during the night (or a burning glass during the day). The match used isn't even an old fashioned "lucifer", but a modern safety match, which was invented even later, in 1844, a year after the fax machine was invented
Nightmare Fuel: Igraine appears to Uther as a hallucination in the third season, dripping with water and screaming: "PLEASE!"
The Doracha. Their appearance is not that frightening, but the idea of them is: undead, unstoppable spirits that can kill with a touch.
Herald of a New Age. You'd think that one of the Knights of the Round Table dripping wet would be a turn on. Not so much in this episode.
On that note, the way that he kills Agravaine and his guards is very chill-inducing in just how effortless it is for him to do so. Word of God says that this was the intention, and it shows in Colin Morgan's performance.
Gwen being mentally tortured by the Dark Tower. Remember the mandrake root from earlier? There's rooms full of them. And there's ghosts screaming in the halls all night.
In The Kindness of Strangers, Morgana makes the skin grow over a knight's face until he suffocated. The actual deed is not shown, but we see the results.
One-Scene Wonder: George, the servant who temporarily replaces Merlin when he disappears.
Mary, the tavern keeper from Gwaine who hits on Merlin.
Grettir and the Fisher King from The Eye of The Phoenix.
One True Threesome: Merlin/Arthur/Gwen is practically canon. With the three of them destined to rule Camelot together, the writers have created Ho Yay between Merlin/Arthur, established Official Couple status between Arthur/Gwen, and provide plenty of friendship between Platonic Life Partners Merlin and Gwen. A recent dream sequence showed Arthur crowning Guinevere queen whilst Merlin watches with a look of abject adoration on his face.
Gwen also originally had a crush on Merlin, who was oblivious, but obiviously admired her and recognized to Lancelot that he found her admirable and very beautiful.
As of A Lesson in Vengeance, it's revealed that Arthur and Gwen take Merlin with them on their wedding anniversary. Think about that for a minute.
Deconstructed with Princess Mithian, who is in every way a completely perfect match for Arthur, except for one tiny problem - he's in love with someone else.
Relationship Writing Fumble: As of the revelation that Arthur and Morgana are half-siblings, much of their interactions in series one borders on Brother-Sister Incest. Word of God states that the writers specifically backed off the Arthur/Morgana ship in order to avoid these implications, though it's uncertain whether this latest reveal was thought of as far in advance as series one. As it stands, the flirting and lingering glances of the first season now seem rather squicky, and there are sure to be some rather ticked-off shippers.
Retroactive Recognition: Most of the guest stars on the show are already established actors, but at least one went on to greater recognition elsewhere: Holliday Granger, who played a Monster of the Week back in season one, and is now widely recognized as Lucrezia Borgia on The Borgias.
Ron the Death Eater: Guinevere in her new story arc gets a lot more grief than she deserves for her actions, considering they are the result of magical brainwashing and most likely additional mind enslavement rather than her own free will.
Rooting for the Empire: Quite a few viewers want the magic users who fight against Camelot to win because they have justifiable reasons, and Arthur while honourable and sympathetic arguably does not measure up to what he's promised to be.
Morgana and Morgause in are curious examples. Morgana was presented as a good-natured and sometimes heroic character for the first two seasons but made an abrupt Face-Heel Turn between seasons 2 and 3, returning essentially as a pantomime villain without a trace of the original Morgana. As such fans rooted for her because a) they hoped she would eventually be redeemed and b) the writers appeared to have forgotten that she was previously good. Morgause got this because she was just so dang cool. Fans also leapt on the season 2 episode where she tried to kill Uther by putting everyone else in Camelot to sleep. However they also forgot that she had attempted to manipulate Arthur into murdering him in her previous appearance and that she was clearly trying to kill Uther for her own selfish desires rather than the good of the kingdom.
Cendred, whom Morgause teams up is depicted some what sympathetically in the series. He seems to be a decent ruler who (unlike Camelot) can muster a huge army and is willing to retreat when it's clear the battle's lost. His relationship with Morgause is sweet and he only loses because of trusting her. Some fans found that they wished he had won.
The Scrappy: Agravaine. Reasons include having no coherent backstory or discernable motivation, taking up a disproportionate amount of screentime, making Merlin, Arthur and occasionally Morgana look like idiots, and being Obviously Evil. Furthermore, many fans were squicked by his lecherous behaviour around Morgana and Guinevere, annoyed that he played such a pivotal role in Uther's death, and unimpressed by his death scene.note It was meant to demonstrate Merlin's dark side by having him deliberately kill a man in cold blood, but it was hardly any worse than Merlin's previous kills: he had been cheerfully killing the likes of Mary Collins, Edwin, Sophia, Aulfric, Nimueh, Morgause, Grunhilda, Myror, Hengist, and dozens of other villains over the last three series, not to mention his poisoning of Morgana and the attempted (indirect) killing of Mordred. The fact that there was no confrontation between Arthur and Agravaine post-betrayal was another disappointing oversight.
Aithusa, we never found out what caused him to become attached with Morgana.
Seasonal Rot: Series 4 & 5, due to the writers not caring about previous plot details like Arthur knew his mom died due to magic, when in Series 2 Uther went to great lengths to hide that fact, and the Dragon's prophecy dying because of Mordred becomes that Arthur will die on the fields of Camlann by a druid's hand. Also the dream of Morgana's death in Series 4 is nothing like her death in the finale. That and Arthur can't remember Mordred at all. Not to mention the whole Aithusa debacle.
Ship Mates: The three most popular pairings and their adjacent "ship-mates" work thusly -
Those that ship Official Couple Arthur/Guinevere are often just as supportive of Merlin/Morgana.
Those that ship Ho-Yay-tasic Merlin/Arthur either support Lancelot/Guinevere or take the Het is Ew angle and ship Guinevere with Morgana.
The Arthur/Morgana lot usually Pair the Spares: Merlin with Freya and Guinevere with Lancelot. Ironically, these couples have the most credence when it comes to Arthurian legends, but have more or less been sunk by canon.
Ships That Pass In The Night: Even before their brief interaction at the end of season 3, there was a surprising number of Morgana/Leon shippers.
Gwaine/Mithian seems to be picking up some steam, despite the two of them having never interacted (yet).
Ship-to-Ship Combat: The fandom used to be quite harmonious until season 2, when the Arthur/Guinevere ship kicked off. The main division in the fandom is now those that love the ship and those that (despite the inevitability of the future Pendragon marriage) wanted Merlin/Arthur or Arthur/Morgana instead. They cite bad writing, lack of chemistry and certain comments made by cast members as their reasons for disliking the ship, while supporters cite the improved writing of the couple in season 3, the sincere performances of the actors involved, and Arthur/Guinevere's Official Couple status.
Squick: Season 2, episode 6. We did not need to see Uther go to bed with that.
Strangled by the Red String: Arthur/Guinevere , one that has led to something of a Broken Base among the fandom. Basically, neither Arthur nor Guinevere interacted very much in season one, although the scenes that they did share had a strong emotional punch to them (Arthur comforts Gwen after her father's death, Gwen tends Arthur on his sick-bed, etc), but come the second episode of season two, Arthur stays at Gwen's house for a short period of time and impulsively kisses her when the time comes to leave. From this point, there are several rather overwrought declarations ("I care about her more than anyone!" and "Anyone who spends five minutes with you can see how you feel about each other!") that don't feel particularly earned, as well as violins, slow-motion, and dramatic back-lighting whenever they're together (and at least one True Love's Kiss). The level of chemistry between the actors is entirely a matter of opinion, but because there are at least two opposing ships on the show, it's difficult to separate what could fairly be described as Strangled by the Red String from the Die for Our Ship attitudes of some fans who are just looking for an excuse to dismiss the romance. In any case, things calmed down a bit in the third season when Arthur/Gwen were given more of a chance to flirt and have actual conversations, and no one could doubt the talent of the actors involved, arguably making this a case of Strangled by the Red String that is nevertheless pulled off by the sheer effort of the actors.
It also happened to some extent with Merlin/Freya. A Rescue Romance that begins with Merlin saving Freya from a Bounty Hunter suddenly has the young warlock willing to give up his entire life in Camelot to run away with a girl he’s had exactly three short conversations with. The only reason he doesn’t go through with it is because Freya didn’t survive the episode. Lancelot and Guinevere could easily fall under this trope as well.
This is played with (usually consciously) with King Uther. The man hates magic due to the fact that it killed his wife, and his genocide of all those who practice magic, no matter how benevolent, is seen as terrible. And yet, most the time the threats against Camelot are entirely magical in nature (though in turn, many of Camelot's magical enemies are striking against Uther out of vengeance of what he's done to them). It's a vicious circle.
Other times, Uther has to make tough decisions about how to rule, and though he's often portrayed to be in the wrong, it's not difficult to see his point when he refuses to help a small village in a neighbouring kingdom because sending armed knights in to help might be construed as an act of war, or when he cuts off supplies from the lower towns during a famine because he needs what little food is left to feed the knights and thus maintain Camelot's safety.
That first one falls through in the Series 2 finale, when its revealed that while he was unwilling to risk war on account of a peasant village getting wiped out, he was willing to send soldiers in order to exterminate the last dragonlord, who at this point was completely powerless, was outside his kingdom, and if anything had only helped him. Balinor's initial willingness to let Camelot get wiped out is Disproportionate Retribution, but can you honestly blame him?
Tastes Like Diabetes: Gaius telling Merlin he's like a son to him. Uther telling Arthur he's proud of him.
They Wasted a Perfectly Good Character: Nimueh was an interesting character with plenty of mystery and backstory left to be told when she was unceremoniously killed off with a bolt of lightening.
Aredian, a witchfinder played by Charles Dance who was one of the memorable non-magic threats with a murky backstory and history with Gaius had a lot of potential drama.
Most of the Knights like Elyan, Percival and Gawaine, they were mostly in the background after their introductions.
Tristan and Isolde, a smuggling Battle Couple who were introduced in the finale of season 4, could have been a really interesting addition to the supporting cast. Instead, Isolde is killed for pretty much no reason other than to provide Tristan with angst, and Tristan is never mentioned again.
Surely more could have been down with Gwen's treacherous handmaiden Sefa, either before or after she's exposed as a spy. She gave Gwen the opportunity to interact with another woman, she had interesting bonds with a variety of other characters, and she was sympathetic in her own way. In particular, her feelings toward Gwen after what happened to her father and what she planned to do about it could have made for an episode in itself.
Too Cool to Live: Ruadan. Finna. Isolde. Aglaine. Alator. Balinor. Kara. The writers were way too fond of this trope.
Uncanny Valley: Gaius' smile in season 2, episode 12, when Merlin tries to wake him up. SO. CREEPY.
Some viewers felt this way about Isolde, with her strange little smile and her tendency to not blink.
Mordred's huge eyes enhance his Creepy Child vibes a lot. The producers mention that they were enlarged with CG in the DVD commentary for his introductory episode.
The... thing that finds Gwaine in the first episode of Season Five does seem benevolent from what we've seen of its actions so far, but it looks creepy.
Values Dissonance: Inverted. By today's standards, Uther is a ruthless tyrant. By medieval standards, he would have been positively benevolent (especially compared to the likes of Cenred). Lampshaded in-show in To Kill The King. Merlin says that Uther is a horrible king for executing everyone he disagrees with, while Gaius points out that Uther ended a civil war and brought peace and stability to the land.
What Do You Mean, It's A Family Show?: Merlin is primarily marketed as a family show, and it has stayed that way for its entire run. Yet they are constantly toeing the line on how much they can imply. They can't say the word "sex"? They have a scene where Uther says that a lord's wife was lonely, and that lord's daughter is his own. They can't do incest? Well, they'll have this UST relationship between Arthur and Morgana in series 1, then reveal that they're brother and sister in Series 3 after they've both moved on. Violence? The huge amounts of Gory Discretion Shot and Bloodless Carnage should give you some indication of just how much they manage to get past the radar.
The last two series originally aired in a later timeslot (after 8 PM) in the UK compared to the earlier times for the first three series (although this was at least partly to do with the unmovable live two-hour show airing beforehand).
What Do You Mean, It's Not Symbolic?: When Aithusa first hatches, Kilgharrah says that he's a good omen for the future of Albion. A few years later, this "good omen" is sick and malnourished, perhaps to indicate that Arthur's death is imminent.
The Woobie: Merlin in the second series finale learns who his father is, meets him, and then about five minutes later has him die in his arms after taking a sword aimed at Merlin. And this is just piling it on: in the preceding episode, he ended up having to poison Morgana, one of his good friends, and doesn't know if she's alive or dead, and a few episodes before that, he fell in love only to have Arthur unknowingly kill his beloved. Poor guy needs a hug.
His Woobie status in that episode was somewhat diminished by the fact that he had just deliberately released a dragon who then explicitly killed hundreds of innocent people, yet the majority of his angst in that episode revolved around his dad. Instead of the fact that he'd, again, caused the foreseeable deaths of hundreds of innocent people.
Morgana throughout series 2. Her terror at her magic being discovered is palpable, and it takes a heart of stone not to be affected when she begs Merlin for understanding in "The Nightmare Begins."
As of Season 5, Aithusa. The poor thing has been locked at the bottom of a well for two years, and is sick and malnourished. When Merlin meets her, she attacks him and has to be calmed down like a wild animal. She's so traumatized she can't even speak, and from the way she was hopping, she might be unable to fly.
Writer Cop Out: Season 2, episode 8: Sins of the Father. Arthur learns the true circumstances of his birth through an entrantress and charges back to Uther, fighting him to the death. Things came so close to changing Status Quo Is God: Arthur was this close to believing that not all magic users are evil, Uther was so close to having to be accountable for his actions. But no, Merlin gives a speech that the sorceress was lying and keeping Status Quo Is God. Colin Morgan gave one hell of a performance to sell it though.
Though it looks to be receiving an interesting pay-off come Season 4, now that Uther's dead and Arthur is blaming magic for it... and not without some justification for it.
Another example would be Morgana's character development. She started off as a more caring person in both season one and two, who wanted to make life better for people like her in Camelot, and now she is sadistic and cruel, willing to hurt anyone to get what she wants. It looks like the writers just wanted to create time skips for season three and season four so they could skip the process of character development, and immediately make her a villain.
Though there are interesting hints in season 2 that she treats people depending on how much she cares for them and is versatile in her judgement of concepts and people. Had it been developed progressively and more on-screen, it would have made her shift into villainy much more organic.