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.
Mark Simmons is undoubtedly the most knowledgeable member of the English-speaking Gundam fandom, and has even done some work for the franchise in helping iron out official translations. He regularly takes part in the fandom, especially in technical discussions, and his website is probably the single greatest source for Gundam info in English, including the official English Gundam site.
He's even gotten some nods within the franchise: Mark Simmons is the default name for one of the Create-A-Characters in the video game Encounters in Space, Gundam SEED has a minor character (a mobile suit engineer) named Erica Simmons, and G-Saviour's main character, Mark Curran, has a sidekick named Simmons.
Broken Base: The fandom is generally grouped roughly based on which series brought you into the fandom, though this has died way down since Gundam's heyday in the early 2000s. The original split was between UC purists and Wingers, with a smaller faction of Seedlings arising later. Gundam 00 was divisive due to its much more Super Robot-styled Gundams and the First Contact plot of the movie given that Absent Aliens has long been a hallmark of the franchise. The newest series, Gundam AGE, has caused some disagreements over its "kiddie" styling.
Complete Monster: Every shows needs at least one super bastard with no redeeming qualities whatsoever, from Gihren to Desil. The most popular is undoubtedly Yazan.
Continuity Lock-Out: The main reason for the shift from the UC timeline to alternate universes.
Crowning Moment of Awesome: The 30th anniversary short "Gundam Perfect Mission", where the protagonist Gundams from every anime up through Unicorn work together to get the Core Fighter into space, where it forms into the original Gundam, the whole thing ending with a Yeah Shot.
Deader than Disco: Gundam SEED's success would spawn a sequel and a manga spinoff series, and even started talks that the CE timeline could become the new UC. However, Destiny didn't work out so well, and a planned movie to wrap up the saga is in Development Hell, making creators and fans give up on the saga and move on to Gundam 00. Today, if you ask Gundam fans of their opinion of Seed, you will get plenty of contradicting responses, and you certainly won’t find many fans of Destiny.
Though the new remastered version of Seed that's currently coming out may change that.
Fanon: The fandom is quite good at creating it, given how many Alternate Continuity versions and contradictory source materials there are.
A similar phenomenon is going on in Gundam Age. Fans who are rooting for Vagan,formerly known as the UE, tend to call out the Earth Federal Forces as corrupt and genocidal. At the same time, they tend to stay mum on the fact that the "oppressed martians" kill millions of innocent civilians, many of whom lived in colonies that were never protected by the Earth Federal Forces to begin with.
Also, some fans will rage against one continuity for having newtype ripoffs, or Char Clone, overly simplistic messages and what have you, and yet will turn a blind eye to it when such themes are re-used ad-verbatim in the original Universal Century timeline.
On the other side, some fans will brand whoever complains about alternate continuities with Double Standards. Complaining about Universal Century, however, is totally OK. Mobile Suit Gundam Unicorn is well-received? Ha! Maybe it's only because it's a Universal Century series! Mobile Suit Gundam 00 is well-received? Of course, it's a really good series! Yeah...they're much more open-minded.
Just Here for Godzilla: Why some fans enjoy the franchise despite finding the plots boring and the characters irritating. It's still got giant robots blowing each other up!
Misaimed Fandom: Yes, the Federation has corrupt leaders. Yes, Zeon has many good, moral, people who serve it. Yes, the Titans are bad. That being said, it's a little scary how many fans will knee-jerk a SIEG ZEON for a regime that murdered, not millions, but BILLIONS of people and continued to wipe out metropolitan centers every few years... FOR FREEDOM.
Rooting for the Empire: For UC, Zeon has far more vocal fans than the Earth Federation. In CE, just mentioning it in reference to the Earth Alliance or ZAFT is likely to cause a Flame War over who was really the bad guy. Ditto, though to a lesser extent, for Mobile Suit Gundam 00. The same debate over whether Vagan or the Earth Federal Forces is worse in Gundam Age is getting ugly as well.
They Changed It, Now It Sucks / It's the Same, Now It Sucks: The series often gets complaints that the Gundams all look way too similar to each other. Yet when they went with going with a very different design approach in ∀ Gundam by bringing in American Syd Mead, it was met with heavy derision from the community.
True Art Is Angsty: Zeta Gundam, while having one of the bleakest endings in all Gundam, is generally considered to be one of the best of them all. Gundam 0080 is similarly dark, and similarly exalted. On the other hand, ∀ Gundam is also considered to be among the best, and it's arguably the happiest Gundam series. Ditto for Crossbone Gundam another series that avoids the Kill 'Em All status Tomino is infamous for. Incidentally, Tomino wrote all three series.