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.
Complete Monster: Arch-EnemyDormammu (also known asThe Dread One or Dread Dormammu or Dread Lord) is the ruler of the Dark Dimension, where he established a dictatorship with his sister Umar, whom he has attempted to destroy on more than one occasion. After Strange bested him once, Dormammu has never stopped brooding on that slight and has endlessly attempted to destroy Strange and everything he loves. The obliteration of Earth and its people have been attempted by Dormammu, but those who survive his conquests have it far worse. The Dark Dimension is run like his personal hell, the denizens enslaved and tormented constantly, with only a small resistance against him. To oppose Dormammu is to risk the endless torture of your soul should you fall into his hands alive. He remains one of the few of Strange's many otherworldly foes to have earned the sorcerer's hatred.
At the end of the "Great Fear" storyline, Nightmare and the Dweller in Darkness have dissolved their partnership and turned on each other. They're too evenly matched in power, however, so fellow demon D'Spayre—who by his own admission is much weaker than either of them—suggests a contest. He'll side with whoever proves better at scaring the populace of Earth. They agree, since even D'Spayre's power would be enough to tip the scales for the winner, and they immediately set about mystically terrifying the whole planet. This goes well at first, and all the fear generated powers up both demon lords. But then suddenly all that power goes away. They did their job too well, and the people of Earth are no longer experiencing fear but despair. So guess who's getting all that power now? D'Spayre is now so incredibly powerful that both Nightmare and the Dweller immediately flee the dimension, and even Doctor Strange can't hurt him. He's normally a Smug Snake, but for that one story, D'Spayre was a Magnificent Bastard.
Dork Age: Strange was changed to be more like a typical superhero in the 1970's. It didn't work.
Not to mention the mid-90's period when he was changed into a young, long-haired business executive who didn't have any of his previous supporting cast with him.
Fridge Horror: Strange isn't virtually omnipotent anymore, but all of his old opponents still are, and there is no hero with both the scale of power, skill, and stability to reliably stand against them anymore. Brother Voodoo, The Sentry, and Molecule Man are dead, Legion is insane, Scarlet Witch is recovering but still mentally fragile, Wiccan is still coming into his power, Hulk is a one-trick pony, generally nowhere near his infinite upper levels of power, and insane, Franklin Richards is still a child, The Mighty Thor doesn't possess the Odinforce anymore, The Incredible Hercules only briefly possessed that scale of power, Nico Minoru is too inexperienced, and powerful as the Silver Surfer may be, he couldn't even make Dormammu notice his attacks. Finally resolved with the end of Bendis' New Avengers, which saw him restored to his title as Sorcerer Supreme. Though the idea of a Sorcerer Supreme — one solitary man or woman protecting the Earth against unspeakable threats — is scary in and of itself.
The entire lengthy run in Strange Tales vol. 2 which finds Strange becoming, very unwillingly, a dark sorcerer, leaving a trail of broken hearts and shot dogs behind him, in order to save the world.
Baron Mordo dying at peace and rising up to the arms of the Ancient One.
What Do You Mean, It Wasn't Made on Drugs?: Early Dr Strange comics were quite popular with student and hippies due to their groundbreakingly surreal artwork. This led to many readers think the artist was on drugs - anyone more familiar with Steve Ditko knows this was definitely not the case.