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: The Colour of Magic
Big Lipped Alligator Moment: The part where Rincewind accidentally teleports himself and Twoflower onto an airplane in our world and ends up thinking that he is Dr. Rjinswand, (33, a bachelor, born in Sweden, raised in New Jersey, and a specialist in the breakaway oxidation phenomena of certain nuclear reactors [a fancy way of saying that they're uncontrollably on fire])... only for the Luggage to interrupt the whole scene.
Becomes Fridge Brilliance when you realize that it's all an extended pun: They were transported to another plane.
Also an Early-Bird Cameo for Roundworld, once The Science of Discworld makes our world a canon part of the Verse's reality.
Harsher in Hindsight: The plane being hijacked by a swarthy, bearded man. At the time, airplane hijackings were most often done by escaping criminals trying to get to a country they could seek asylum in. The act didn't become associated with Muslim extremists until the late '80s.
Hilarious in Hindsight: Rincewind muses on how there are too many heroes in Ankh-Morpork, and how the notable questing-grounds are so busy during high season that they plan to introduce a rota. A scene familiar to anyone who ever played a regular MMORPG, all of which came out well after this book was published (with the exception of certain MUD games).
Plus, the troll encounter plays out exactly like a random encounter in a console RPG.
Moral Event Horizon: Galder Weatherwax trying to outright kill his former student via magical arrow in the film. I mean, he had to take the spell back by force but that is harsh.
Special Effects Failure: In the two-part film from SkyOne, please pay no attention to Cohen's clearly visible teeth.