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: Many Western Digimon fans do not know that the series started off as a spear counterpart of the Tamagotchi, or even that the Digimon franchise had a pair of manga, a short film, and at least 3 video games before the premiere of Digimon Adventure.
Archive Panic: 332 episodes, 9 movies, 6 manga series, and 22 video games. If you want to experience everything, good luck.
Canon Sue: Ryo Akiyama, who is a significant figure in two pieces of Digimon canon (the two-part Adventure series and Tamers), and in his home games, he leads whole teams of Digimon composed of all the other main characters' partners in battle, and can keep them all at Mega Level. On top of that, in Tag Tamers and D-1 Tamers, he's actually V-mon's partner pre-Daisuke.
Ear Worm: The English theme of the first three seasons.
Evil Is Sexy - A few humanoid evil digimon can qualify as this.
Fan Dumb: Fans of the Anime series have a tendency to declare all information from the V-pets and Video Games non-canon. Never mind that these products are produced by Bandai themselves and the the plots to several of the earlier anime series are tied into the plots of the video games.
Just Here for Godzilla: In an amusing inversion, there are several fans who don't really care about the Digimon and just watch for the interaction between the human characters.
To clarify, the first antagonist ever was was the brat Shinichiro in the C-mon one shot, there were organizations of human hackers in Digital Monster Version S who served as the primary antagonists, V-tamer 01 had a handful of hostile tamers, in Digimon World we have Anologman, another hacker, who is also the primary antagonist (and responsible for the creation of Mugendramon, the most powerful digimon).
Similarly not many people realize the term "Tamer" has been used to refer to a child with a digimon long before the release of Digimon Tamers
Pandering to the Base: Every series contains a clear expy for Agumon and Greymon. A hot-headed lead, often sporting goggles and an introspective foil with a canine partner are common, though not present in every incarnation of the series. Said draconic and canine digimon will get all the screentime in the later series, while the other digimon and their tamers will usually serve as token team mates.
They Changed It, Now It Sucks: Many Western fans blindly reject new series simply because they're different in design and aesthetic from Adventure or Tamers.
Toy Ship: Rampant everywhere, thanks to there being about 30+ kids throughout the franchise.
Ugly Cute: Some Digimon pull this off—mostly younger level ones but some older level ones, too.
Unfortunate Character Design: WarGreymon has this in spades. He has a mostly human anatomy. He also eschews pants in favor of a skimpy black banana hammock. The front of said banana hammock features a piece of armor with a very suggestiveshape.
Woolseyism: Some of the changes of Digimon are actually a little more liked amongst the English-speaking community. Part of it is Nostalgia, but even after seeing subtitles, some actually still prefer the English names.
Most commonly, Myotismon - adding in a bit of a Genius Bonus. A good number of fans still prefer Crusadermon to LordKnightmon, and even like that Frontier made the feminine looking pink-armour-clad knight female. Similarly, Duftmon was localized as "Leopardmon", which given its "Leopard mode" actually makes a lot more sense. GuardiAngemon as well, due to sounding more like "Guardian Angel" rather than "Slash angel".