* AlternativeCharacterInterpretation / WellIntentionedExtremist: Queen Mab acted completely selflessly througout; her entire plot was an answer to the woman's prayer in the beginning, who cried "Queen Mab!"; It was an ordinary British human who prayed for the Old Ways to come back.
** Merlin, meanwhile, spends the film on a vengeance quest to destroy an entire religion because he's angry at one goddess (though he knows that the other members of the pantheon are good), becoming a knowing accomplice to a rape in order to help achieve his goals. He then complains that men don't live up to his lofty moral standards.
* BigLippedAlligatorMoment: The cutaway scene of Queen Mab and Frik dancing (for a very loose definition of dancing). The latter you might forgive, but the former...
* CompleteMonster: While most of the villains have some redeeming traits, Vortigern goes all the way. In addition to being a tyrant and a power-hungry conquerer, he takes the daughter of one of his most loyal lords captive and threatens to kill her himself if her father doesn't behave, just because he doesn't trust anyone, and casually refers to having murdered men, women, and children just for mouthing off to him.
** Mordred is even worse. He injures or murders castle servants while practicing archery, shoots arrows at everyone in the room just because one of them commented that his performance was "less than perfect," acts disturbingly excited and pleased at the thought of Elaine's heartbreak, laughs at his own mother's death, starts a war and plunges Britain into chaos, etc. In the novelizations, his evil is stepped up a notch, and his motives border on ChaoticEvil OmnicidalManiac doing it ForTheEvulz.
* CrowningMomentOfFunny: Shortly after Morgan le Fay dies, Mordred comments, “She sleeps alone, at last.”
** The second time we see Vortigern's castle under construction collapse:
--->'''Architect:''' The foundations are as strong as-!
--->*camera shifts to Vortigern's face, we hear the castle fall and see rocks tumble down the cliff in the background, and Vortigern's suppressed rage*
--->'''Vortigern:''' *DeathGlare* ...you were saying?
* CrowningMomentOfHeartwarming: Several. Just about every one is also a TearJerker, though.
** One specific example is Merlin telling Arthur, "you were the right man to hold Excalibur", and seeing the look of gratitude on his face, [[spoiler:[[TearJerker moments before he dies.]]]]
** Another occurs between Morgan and Frik, after their magic has slipped away and both are back to being homely:
-->'''Morgan:''' Frik, my love, am I still beautiful?\\
'''Frik:''' Beyond words, my love. Am I?\\
'''Morgan:''' Oh, yes. Beyond words. [dies]
* EvilIsSexy: Queen Mab.
** If forgetting Queen Mab is the only thing that can ultimately defeat her, then isn't Merlin shooting himself in the foot by spending the rest of his life telling stories about her?
*** Though it becomes FridgeBrilliance if you consider that the decline of the Old Ways and Mab's death in particular were very bittersweet for Merlin. He may be trying to keep them alive despite himself.
*** In the novelizations, Merlin doesn't include Mab in any of his stories, instead attributing her deeds to Morgan le Fay or Mordred, and Frik does the same thing. This is implied to be the thing that Frik noted was "omitted" from Merlin's story at the end.
*** Maybe he took a page from Terry Pratchett? When you tell stories about something, people ''know'' about them more, but ''believe'' about them less. Tell magical, fantastical stories about the FairFolk today: next stop, nursery wallpaper.
*** There's also the fact that the stories would be telling people about Mab...but that she ''used'' to exist, and would include the ending in which she faded away. So even as they told people of Mab they'd be reinforcing the fact she is just a memory, a thing of the past.
** So, [[spoiler: Galahad]] was the real ChosenOne, instead of [[spoiler: [[TheUnchosenOne Lancelot]] ]]. So, a [[spoiler: 10-year-old boy]] was supposed to win the joust?
*** Had Merlin known that [[spoiler: Galahad]] was TheChosenOne he wouldn't put a kid in a jousting match. Also, it's that he would be the perfect knight when he was grown up, not as a kid. It's not suggested that he has to win a jousting match anyway, just that he has to be a man of pure heart.
** If changing form is just an illusion then [[spoiler: Merlin and Nimue will still be dead in a few years despite Merlin's apparent youthening of them both at the end.]]
*** It's only an illusion when the Fey do it. Merlin used a different kind of magic to do that. It's explained more in the novelization.
** If Frik can see so far into the future as to know about early modern French aristocrats, he should also foresee the inevitable triumph of Christianity in Europe.
*** Time can be rewritten. Presumably that was what he was aiming for.
*** At one time Frik is shown writing fairy tales, so that Mab and he will be remembered. Mab is dismissive of this, but Frik seems to keep all options open. Perhaps he has seen the triumph of Christianity.
* HilariousInHindsight: Just look at the [[http://l6.sphotos.l3.fbcdn.net/hphotos-l3-snc4/hs924.snc4/73703_160452923992985_100000848364812_285470_1298358_n.jpg costume]] MartinShort wore as Frik, and consider that Morgan is played by HelenaBonhamCarter.
** This isn't the last time Lena Headey would play a [[GameOfThrones queen cheating on her husband with one of his knights]].
* IronWoobie: Merlin himself.
* JerkassWoobie: Morgan le Fey grows up insecure about her lisp and drooping eyelid. She witnesses Uther rape her mother via BedTrick, then murder her father and his men, all because Merlin let him. Later, she's used as a pawn by Mab and Frik, and eventually her son completely stops caring about her [[spoiler:in preference for a surrogate, "Auntie" Mab, who kills her in the end.]] On the other hand, her reaction to the childhood trauma is bitterness and eager complicity in the plot to screw over Arthur, and she probably has a lot to do with Mordred's poor character.
* MoralEventHorizon: Vortigern casually referring to having killed men, women, and children simply for insolence, or deciding to [[spoiler: sacrifice Nimue to a dragon]] simply because it was most convenient.
** For Mordred, this moment is probably when Mab [[spoiler: kills Morgan le Fay]], and he responds by ''laughing'' about it and complimenting her on it. “That was very clever.”
* TearJerker: [[spoiler: The deaths of Ambrosia and later Arthur, and their final words with Merlin.]] Also, [[spoiler: How Frik's relationship with Morgan le Fay ends.]]
** The Lady of the Lake's final conversation with Merlin, and the [[spoiler: lingering demise of both Queen Mab and Magic.]]