Badass Decay: Leviathan was one of the most powerful summons in early installments (second to Bahamut in III, the King of Eidolons in IV, one of three level 5 summons in V), but became more of a mid-game summon starting with VII, and is now a part of the 6-pronged elemental wheel seen in the latest installments, alongside "basic" summons like Ifrit and Shiva while his old role was effectively given to Alexander. Final Fantasy XV inverts this by making Shiva and Ifrit more badass and elevating them to Leviathan's level.
Final Fantasy X: The final boss Yu Yevon is something of an Almighty Idiot who doesn't use particularly powerful attacks or defenses (other than one flunky healing him for 9999 damage, but the party can easily outdo that kind of damage). One particularly well-known strategy involves exploiting his lack of Contractual Boss Immunity by inflicting the Zombie status on him, causing his own ally to damage him for quite a bit of damage. This is more or less the point, coming after very difficult battles: Yu Yevon was the driving entity behind Sin's constant regeneration and destructive impulses, but over millennia became entirely helpless without an Aeon to possess and turn into Sin anew.
Contested Sequel: Every Final Fantasy game somehow manages to become more controversial than the last one.
Critical Dissonance: The entire series. Critics almost universally give Final Fantasy games high scores. Fans on the other hand are a heavily fragmented Broken Base. Name any game in the series and, though the proportions will vary, you will find people who hate it, those who love it, and those who don't feel strongly either way.
It is generally agreed that the series has done this, but there is no absolute consensus to when this happened, being the subject of massive Flame Wars. General consensus is it happened somewhere from IV to VII (and old-school Japanese fans would readily assert III, but all non-Japanese fans missed that particular boat). Each game in that span, in their own ways, radically improved upon the gameplay, plot and/or characters compared to what came before.
It is also generally agreed that the A Realm Reborn relaunch of Final Fantasy XIV signified a second beard-growing in The New '10s. While there have still been debates about some of the games that followed, in general ARR's launch in 2013 marked a general improvement in the quality and effort put into Final Fantasy titles, with XIV itself taking a major lead position with its expansions.
Hilarious in Hindsight: A commonly believed though untrue story behind the series' title; it was called "Final Fantasy" because Squaresoft was going bankrupt and everyone in the company expected this to be their last game, and Hironobu Sakaguchi was considering giving up being a video game designer and decided to let this game decide for him. Instead the game was hugely successful, saved the company and Sakaguchi's career, and is now a pillar of the JRPG genre.
It's widely believed that the reason Square took the franchise to Sony was because of Nintendo's insistence on using Cartridges for the Nintendo 64. Over 20 years later, Square Enix announces they're porting VII, IX, X, X-2, and XIInote along with Crystal Chronicles, which did come to the Gamecube to a Nintendo system for the first time, specifically the Nintendo Switch, which is Nintendo's first cartridge-based system since the N64.
People think that the pretty, angsty protagonist only started happening when the games moved onto the Playstation. Either they do not know about Cecil Harvey, or they are actively practicing denial.
Percentage-based damage. The Gravity spell family—which first appeared in Final Fantasy V—is the most famous example of this: Gravity takes 50% of the enemy's HP, no matter how much HP he has. However this first appeared all the way back in Final Fantasy II with the Blood Sword, which always took a certain percentage of the enemy's HP, no matter how large it was.note The Blood Sword is unusual in that unlike just about every other percentage based function in gaming, it always did 1/16 of the target's max hp per hit. It was also possible to hit 16 times per turn, meaning it could easily OHK anything and everything.
Popular with Furries: Red XIII from VII, Kimahri from X, the Bangaa race, the various Behemoth breeds, and some of the summon designs ensure that a lot of anthropomorphic fan-art surrounds the franchise.
Tetsuya Nomura became this trope thanks to being the Creative Lead of the Compilation of Final Fantasy VIInote A Slew of Spin-Off titles focusing on expanding Final Fantasy VII. that was a major focus of the company in the early 2000s. When VII became a huge hit, Nomura not only became the go-to artist for many subsequent main series titles, but he became director and producer of several Compilation titles, and fans began to blame anything wrong with the series on him. This is despite the fact that outside the Compilation, he had only ever been an art and character designer; some 2010s-era games begin to credit him as a Creative Producer, but the hatedom for him existed long before then.
After Final Fantasy XIII came out, fan attention for the trope shifted to Motomu Toriyama. Many fans see him as a Trolling Creator and blame him for the poor quality of the XIII trilogy. A bit more justifiable than Nomura, as Toriyama is the director of those games and thus does merit blame for their quality. It remains to be seen how any future projects he's a part of, or just future titles in general, will uphold this status.
When Final Fantasy XIV was first released in 2010, it was panned heavily from critics and players alike for being full of glitches, having illogical gameplay mechanics, and having a lot of Cut-and-Paste Environments. Hiromichi Tanaka was the director at the time and was also the director for Final Fantasy XI. Tanaka got the blame for the failure that Final Fantasy XIV went through, which resulted with him being forced out of Square Enix (with a note that he had been one of Square's founders in the 1980s. Although he was rather famously awkward with the news media in general and made some specific gaffes during the initial press cycle for XIV, some fans of the 1.0 game feel Tanaka was made to take the fall for a disaster that had a lot of responsible parties.
Sequelitis: Much like the beard-growing detailed above, it is frequently argued by some that somewhere between the very late 90s and through to about 2010 (with the release of the original XIV and Final Fantasy: All the Bravest), the franchise began to suffer quite badly from a case of sequelitis (with the aforementioned examples being extreme expressions of the malaise). Much like the beard-growing, however, precisely when the franchise began suffering serious issues, or whether the problem has even been entirely consistent, is one of the most mileage-varying topics one can discuss in the fandom (with a real risk of discussion becoming Flame Bait).
Silent Majority: These games are best-sellers, but you would not know this by looking around the internet, though. Before examples were removed, the Final Fantasy fandom was listed as an example of the fans who still buy the games and enjoy them, but don't feel the need to scream about it on the internet.
True Art Is Incomprehensible: As the series progressed, plots became increasingly complex and convoluted... and the individual games got more and more critical praise. VII is considered one of the greatest games of all time, nevermind that its plot is very confusing and was not translated very well to boot. Subverted with some later games; critics and fans have begun to single out poor and confusing plotlines as a weakness of the series.
Visual Effects of Awesome: Alongside Awesome Music, this is the other trope that most fans universally agree on, ranging from the elaborate opera scene and destruction of the world in VI, to the warping antics and titanic Astrals in XV. The most common ground for these are a) the ever-present summons, and b) the more recent fight scenes.