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.
YMMV: Magi - Labyrinth of Magic
Abandon Shipping: The few fans that supported Kougyoku in her crush, jumped ship quickly after the reveal in chapter 212.
Alas, Poor Villain: Pretty much any villain's death. The Black Rukh can only survive in someone who has cursed their destiny and this normally happens through great tragedy.
Angst? What Angst?: Despite having been locked in a room with no one but a Djinn for most of his childhood, Aladdin shows very little signs of mental strain over this outside of flashbacks.
Arc Fatigue: The fight against the Medium throughout the climax of the Magnostadt Arc ended up as this trope. Several Padding skirmishes against the Medium, which amounted to nothing more than the continued use of the Worf Barrage, takes place so that over time, more and more of the manga's major characters enter the scene up until the point where literally every named character introduced the past 200 chapters are on the scene. Ironically, the Medium is defeated just moments after the last primary characters, Judar and Hakuryuu, appear.
Chaotic Evil: Judar. He's rather blasť about the consequences of his actions and just likes to stir up violence and chaos.
Complete Monster: Jamil, Morgiana's former slave owner, shows little redeeming qualities as he constantly abuses Morgiana and Goltas for no reason. There's also his unparalleled arrogance.
Empress Gyokuen of the Kou Empire appears to be a sweet, caring and gentle mother. The truth is far different. Gyokuen is a member of Al-Thamen, and is one of its oldest and most powerful members. To achieve the throne, Gyokuen married the Emperor and bore him four children. She later had her husband murdered, along with two of her sons, with her youngest, Hakuryuu, barely surviving. When he asked Gyokuen if she was really behind it, Gyokuen asked him what he would do if it was and taunted him over how powerless and unable to strike back he was. She also offed her second husband in a thoroughly disgusting fashion for no reason other than that he stood between her and the throne. During the Magnostadt arc, Gyokuen takes the initiative in fighting the heroes with her forces, revealing herself as a former Magi of King Solomon, who she betrayed for Al-Tharmen. After summarily deciding the world is a 'failure', Gyokuen uses the lives of others to summon the 'Father' of Al-Tharmen to devour magic from the world and let it die in darkness.
Deus Angst Machina: In the manga, Alibaba is not hostile towards either Kougyoku or Hakuryuu. This was apparently not good enough for the anime writers, who have him spend the entire Zagan Dungeon dealing with his hatred and loathing. The rearranged the entire arc for it, too.
Die for Our Ship: Poor Ren Kougyoku gets lots of shit for her crush on Sinbad. Not to mention the amount of backlash she receives from Morgiana/Alibaba shippers due to what looks to be a slow-budding romance between Kougyoku and Alibaba.
Estrogen Brigade: The author is female, and has included a full compliment of Bishonen and Ho Yay. As a result, the readership for Magi has a pretty even male/female ratio.
Fan-Preferred Couple: The vast majority of fans seem to ship Alibaba and Morgiana. Sharrkan and Yamraiha is pretty popular as well.
On a Yaoi note, Sinbad and Jafar is quite popular as well.
And, then there's Judar and Kougyoku which is also remarkably popular.
Foe Yay: Judar has mentioned many times that he wants to "own" Sinbad.
Freud Was Right: The way Aladdin's flute hangs just above the knot of his pants can look quite suggestive at times.
Fridge Horror: Judar's a Magi who himself has "fallen into depravity", and we know thanks to Aladdin's dose of Solomon's Wisdom on Judar that he was kidnapped and seized by Al-Thamen at birth; now start to think about all the horrible, horrible things Al-Thamen must had done to Judar that broke him enough to curse his fate and become the Psychopathic Manchild he is today.
It's later revealed that Al-Thamen manipulated the chemicals in his mind with Black Rukh, forcefully causing him to fall into depravity.
Genius Bonus: The language of "Torran" is Cuneiform, one of the oldest writing systems and was the main system used by Sumeria.
For that matter, Sinbad. So far, he's been paired with the four protagonists, all his generals, the princes and princesses of the Kou Empire, the other Magi (Judar, Scheherazade and Yunan) , himself....
Les Yay: Leila and Sahsa, especially on Leila's side. She also seems to really like Morgiana, saying she would be sad if Morgiana left the caravan.
Morgiana seems to have this with a lot of girls. Other than Leila, her first interaction with Toto involved being hugged by her with Morgiana's hands on Toto's chest. A special chapter/Omake has Myron from the Finalis corp try to kidnap her "because she's so cute."
Paimon, she says she has fallen for Hakuei while holding her suggestively and in Alma Toran she tells a fellow female Djinn, Leraje, to forget about Focalor and fall in love with her instead.
Memetic Molester: Ithnan, who spends a good long while living inside Hakuryuu's body, then emerges completely naked to compliment him on how comfortable it was.
One look at Aladdin and this will definitely come to mind. He's young, cute, naive... Word of Goddess is that Aladdin was originally going to be female. The Sarashi he still wears is a remnant of the early character designs.
Moral Event Horizon: Ahbmad. He endangers his nation economically, doesn't consider people from the slums to be worth anything at all, including his own half-brother, and is more than willing to sell his subjects into slavery if it means getting more money from the Kou empire.
Sinbad might have crossed this when he showed Alibaba how far he would go to protect Sindria. He is using his djinn to make three people unknowingly spy on their countries for him, one of which is his own citizen. Another is Kougyoku, which if he had used anybody else might have not been so bad.
Narm: The Laem Empire looks like a thin anagram for "lame" and many readers are going to pronounce it that way.
It seems the Fansubs have noticed it and start to use the alternative name "Reim" which, if you think about it, makes more sense considering it's based on Roman Empire.
Ship Sinking: Sorry Alibaba/Morgiana fans, Alibaba found a girlfriend in Toto...wait, nope, Chapter 200 sank Alibaba/Toto. And Chapter 202 made sure that Alibaba/Toto ended up in the depths of the ocean. Then Chapter 203 all but confirms Alibaba/Morgiana, which is soon challenged by Kouen demanding that Alibaba marry Kougyoku.
The odd part is that despite how much the manga content changed here, it still ends up following the manga again when the second season started; one of the few rare occurrences where the anime adaptation fixes itself... though this reaction for going the anime-original route in this portion of the manga still lingers somewhat.