Doctor Strange movie and the comics that started Stephen Strange on his superhero story back in the 1960s.
Given of the long lives Marvel Comics superheroes have led, with most of the classic character dating back nearly 60 years, their personalities and character arcs tend to change over time as new writers emerge to satisfy a new group of fans. There can be very stark differences between adaptations of comic book characters and the plotlines that they follow, and that's certainly the case with Doctor Strange.
Character Consistency
Comic books can't cast actors, but, instead, have many different writers. With so many contributors for a project, the character's personality and motivations can get muddled. However, in adaptation such as Doctor Strange, Benedict Cumberbatch is able to play Stephen Strange with consistency.
Reddit klapaddd cites Benedict Cumberbatch as "the absolute greatest casting possible for Strange". Instead of multiple different authors trying to use their own style to make a single character, it's the actor who takes all these different versions and interprets the character in a way that serves the narrative and justifies the interpersonal relationships.
Mordo
A lot of modern media makes a point to make their villains make sense. It is harder to write a compelling storyline for a villain with no motivation. Mordo could be one of the great characters that are going to be in coming MCU movies.
Part of what makes Mordo such a promising villain is his justification. He feels betrayed by the Ancient One for using the dark dimension powers. Reddit Anomaly_Rue explains that, in the comics, Mordo was "...just evil for the sake of gaining power." It makes him a much weaker villain in the comics compared to the potential he shows in the movie.
A Slow Introduction To Magic
The MCU is a superhero world with a lot of action. So, the new superheroes popping up that have very heavy magic influences, like Doctor Strange, have to tread carefully.
The comic books throw the readers into the world of the mystic arts very quickly because of the entertainment medium. Reddit Carpenterdon points out that "they had to introduce Magic to the general audience in a way that slowly told the story yet kept enough action to hang on to the 'action film' fan." It makes the movie much more digestible to the more casual viewers and set up Strange's plot nicely.
A Divide From The Avengers
Reddit elcapitan520 notes that the world Doctor Strange is invested in is very separate from the avengers' world. They wrote that Strange's style, "doesn't always translate to fighting in this dimension with a team."
This was a smart decision, allowing the audience time to digest the new world they have been introduced to, while still getting to learn about Stephen Strange as a character. Throwing him in with the Avengers immediately would have taken away from his character development and the establishment of the mystic arts.
Kaecilius
Kaecilius is the main villain in the first Doctor Strange. In the movie, he is a much more important character than he ever was in the comics. In the comics, Kaecilius was a disciple of Mordo and simply existed to do his dirty work.
parallels to Supreme Strange, for the What If... series.
The Ancient One's Death
Reddit DaftMemory started a thread that discussed how the Ancient One in the comic books has to be killed by Strange to destroy the alien living in his mind. One says, "I thought it was one of the most beautiful and touching scenes the Marvel movies have put out so far."
It is heartbreaking to read Strange kill the Ancient One, but would not have held up in the movie. Strange didn't have as close a relationship with the MCU Ancient One as he did the comic's version. The impact of her death is much better handled in the movie, instead of relying solely on shock factor.
Dormammu's Defeat
In the comic books, Doctor Strange has to face Dormammu several times as he keeps coming up with ways to attack Earth. Doctor Strange defeats him in a handful of ways, including greater magic and hand-to-hand combat.
Reddit pokeslap, and many others, were happy to see that "Strange doesn't beat Dormammu but annoys him into submission. This was just so clever and interesting to see." It was a different kind of victory then usually seen by the likes of Thor or Iron Man, but possibly even more satisfying to watch.
Wong
Marvel takes pride in their complex characters in their new movies. Often, the side characters will outshine the title character and become fan favorites. One of these characters is Wong, in Doctor Strange.
Wong is a great character that a lot of people really like. So, it may surprise people to learn that Wong is hardly even in the comics, let alone an important player. Reddit Anomaly_Rue points out that "in the comics [Wong's] more of a manservant, while in the movies he is an independent character who is an equal to Stephen" throughout the movie. The movie wouldn't be as good without him.
