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: Most people know about Little Nemo because of the NES Game Little Nemo the Dream Master, which was based on the animated movie (not the other way around). You'll even be hard pressed to find anyone who has heard of the animated movie, and even fewer people know that the movie was based on a comic strip. So the comic strip of Little Nemo in Slumberland suffers from two degrees of adaptation displacement. Not to mention that whenever anyone talks about Little Nemo these days, people assume they mean that Pixar movie with the fish.
Archive Panic: So the strip ran from 1905 to 1923. At roughly 52 pages a year. Wow. You have some reading to do.
Cult Classic: This applies to the film also, and by extension, the video game.
Values Dissonance: In the comic, one strip has Nemo going around giving animals the ability to talk to humans. One male hippopotamus begs him not to let a female hippopotamus talk because "she'll talk to you deaf, dumb and blind about women's suffrage!" (Then again, this was around 1910)
Not to mention the extreme racial caricatures of the natives of Candy Island. But it was 1907.
What's more, a group of the Princess's very African-looking slaves show up to march in a parade in Slumberland.
The Abusive Parents issue. It was normal at the time. It is still normal in some places around the world, and considered the only way to be good parents. Ouch.