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.
Adaptation Displacement: The MGM movie adaptation is much better known than the Oz books. Some of the more recent books set in the Oz universe — such as Wicked — even adopt a few of the movie's more iconic elements, like the ruby slippers and the Wicked Witch's green skin.
This was actually exploited by 2013's Oz: The Great and Powerful. Legally, it's a prequel to Baum's original novel (which is in the public domain), but it was written with the idea that viewers would see it as a prequel to this movie (which it isn't).
Alternative Character Interpretation: ThisCracked article deconstructs the entire movie and makes you wonder whether or not Glinda is in fact the real villain here. The idea is that she's subtly manipulating Dorothy to serve as an assassin, setting her on a path that she knows will directly lead to her killing off all of the Witches who oppose Glinda, as well as end up making the Wizard decide to leave Oz forever. In the end, who is left and ready to assume control as the all-high overlord of Oz? Glinda!
In hindsight fans of the movie have been wondering whether the Wicked Witch really is as bad as she seems. A child came out of nowhere and murdered her sister, so don't you think she'd be upset? The combined with the above interpretation makes the movie quite interesting.
Was it all in Dorothy's head or did the characters all just suspiciously look like family members of her?
"We represent, the Lollipop Guild, the Lollipop Guild, the Lollipop Guild..."
"We represent, the Lullaby League, the Lullaby League, the Lullaby League..."
"Over the Rainbow"
"We're off to see the Wizard, the Wonderful Wizard of Oz..."
"Ding, dong, the witch is dead! Which old witch? The Wicked witch!"
As coroner, I'll vouch for her/I thoroughly examined her./And she's not only merely dead/She's really most sincerely dead.
"We welcome you to Munchkin land, tra la la la la la...."
The guard's Oeo chant. Bonus points for not really meaning anything.
The real brilliance is that it does mean something, if you listen really close you can hear what the guards are saying Oh we love, the old one, oh we love the old one.
Fan Dumb: Quite a few people accuse Dorothy of manslaughter, if not outright murder, of the Wicked Witch of the East, which is like accusing someone of a hit and run while they're tied up in the trunk. They seem to disregard the fact she neither caused nor had any control of the twister that carried her house to Oz.
Fantasy Ghetto: The executives at MGM insisted on changing the ending of the book to make it clear that the Land of Oz only existed in Dorothy's imagination, thinking that no one could ever take a genuine fantasyland seriously. To this day, while no one would ever deny the movie's popularity or influence, many people would argue that it "doesn't count" as a fantasy film because the supernatural events are explained away as a dream.
Fountain of Memes: Dozens memes and tropes have come out of this movie. For decades and decades, it has been referenced in countless shows, movies, books, and other parts of popular culture. It's hard to imagine a movie more ingrained into the public knowledge than this movie.
Fridge Horror/Paranoia Fuel: As if the Wicked Witch wasn't scary enough on her own, they had to add in all the scenes of her watching the heroes in her crystal ball...making it abundantly clear that she can see you wherever you are. And if she wants to hunt you down? She can teleport anywhere instantly. Whenever she wants.
Why was Dorothy running away in the first place? Because Toto bit the owner of their farm and her Aunt and Uncle where threatened with eviction unless Toto was put down. This plot thread is never resolved.
Fortunately, if you view the fantasy elements as real, of course, Miss Gulch turned into a witch during the twister and had a house fall on her...or was melted...it is unclear which witch was which...
Narm Charm: The whole film runs on it, especially to a modern audience.
Unless you're under the age of ten. There's a reason The Wicked Witch of the West is considered one of the scariest villains ever.
Older Than They Think: Movie fans are often surprised to learn that The Wizard of Oz is based on a book that was published in 1900 and the book had sequels published over the span of 50 years.
Similarly, many fans of the movie are unaware that it's actually the third film adaptation of the book to hit theaters. The first was a short film that came out in 1910, and the second was a silent movie starring Oliver Hardy that came out in 1925.
Seinfeld Is Unfunny: Back in 1939, the idea of a fantasy world was very novel to film audiences, so much so that the studio took issue to it (see Executive Meddling). However, countless other works featuring fantasy themes and motifs have been released since The Wizard of Oz came out, leading many modern viewers to accuse it of a poor plot, cheesy acting and dialogue, flat characters, and outdated special effects.
Shown Their Work: Multiple funnel clouds of different types are seen in the distance. The wind is proving destructive long before the tornado gets close.
Vindicated by History: While it did okay when it first came out, much of the movie's popularity was gained in the 1950s with yearly telecasts. Some serious film critics even consider it to be superior to Gone with the Wind, which was released (and won the Best Picture Oscar) the same year.
What an Idiot: The Wicked Witch of the East flying in a tornado next to a house.
Nightmare Fuel: In the episode "Fearless", the Witch is disguised as a gypsy in an amusement park. After Dorothy and the others leave, the park completely changes; the guests are her winged monkeys and all the rides are gone. This happens in only a few seconds, but it's very memorable and a Moment of Awesome for the animators.
In the episode "Not In Kansas Anymore", the Witch tricks Dorothy into going home by making her think Aunt Em is ill. However, she instead creates a fake Kansas for Dorothy, posing as Em in order to get the Ruby Slippers. When the illusion is dispelled, she retaliates by blowing up Dorothy's house.
"Dream A Little Dream" is about this trope, as the Witch invades the Lion's dreams to coax the others into following her. Cue the Lion having nightmares.