In Japan, Mandala Gundam is fairly popular - evidently due to its especially bizarre design. (This backfired when G Gundam toys were released stateside: Mandala Gundam action figures were always the ones left hanging on the shelves.)
Not just Fuun Saiki, Master Asia himself is insanely popular among mecha fans. He even finished runner-up in the SaiGAR 2007 tournament!
Esoteric Happy Ending: While on the personal level it's happy, on the global scale it may not be as happy as it seems. There's another Gundam Fight coming, though the pilots' resolve to preserve the Earth means that it might not be as ecologically-devastating this time round. The tone of the series and the conversation between Chairman Karato and Dr. Kasshu in the finale seems to strongly imply that they will devise a way to make the system less destructive, especially since Dr. Kasshu himself is now free to have another try at creating something that can restore Earth that won't decide to Kill All Humans if it gets a little dinged up on landing.
Blink and you miss it, but the Twin Towers are visible in some of the establishing shots for Manhattan.
Andrew's accusation that the report Neo Russia compiled on the accident that killed his wife was a cover-up is a bit painful to hear after the Russian annexation of Crimea and the subsequent information war between it and the West.
Hilarious in Hindsight: Neo France apparently uses Neo Francs, even though France stopped dealing in francs when it adopted the euro in 2002.
One-Scene Wonder: Some feel this way about the previous generation of the Shuffle Alliance.
So Bad, It's Good: For several fans of the whole Gundam franchise, seeing as how this show is an Oddball in the Series. While there's a sizeable amount of people who enjoyed G Gundam for exactly what it is, there's also quite a few who thought the show was completely ridiculous, and yet love it just as much.
Superlative Dubbing: The English dub hams it up so well that many swear up and down it's far more entertaining than the Japanese audio. On top of that, they kept all of the songs intact.
Vindicated by History: It was the first alternate universe Gundam series, and to this day is the biggest departure from the usual Gundam fare (barring SD Gundam works), and at the time of its release was very divisive for those reasons. As time went on, it has become one of the most unilaterally beloved Gundam series.
Wangst: Domon and Rain's relationship slips into this occasionally, notably towards the end of the series.
What Do You Mean, It Wasn't Made on Drugs?: Some of the Gundam designs are freaking surreal. The director himself said that he was giggling while giving a few of them to the animators. (At least the Skull and Ashura Gundams have a legitimate excuse: they were sent in by kids in a viewer contest.)
What Measure Is a Non-Badass?: Rain had the misfortune of falling in love with Domon at the end of the series. Cue the cries of "Rain lost coolness because of that" from the fans. They consider her "inferior" to Allenby due to being more traditionally feminine than she is and for being the Ms. Fanservice, ignoringhermultifacetedpersonality. Not to mention, Rain fully demonstrated that just because she doesn't like to fight doesn't mean she's not good at it, especially after piloting the Rising Gundam to rescue Allenby from DG Cell takeover.
Chibodee's nicknames for the other fighters are changed from national adjectives, to simply the names of their countries. E.g., he says things like "hey, Neo-Japan" rather than "hey, Japanese", the latter of which is a slur in the States.
Also, the song that Rain and Chibodee's crew sings when he fights Romario. In Japanese, it's the end credits song. In English? AMERICA THE BEAUTIFUL.
World of Ham: This anime is a mile-high ham and cheese sandwich with the works. And it's glorious. Perhaps even more so with the English dub.