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.
Americans Are Indifferent: In Japan, Final Fantasy V is one of the more popular installments, more popular there than Final Fantasy VI. Overseas, it isn't as popular, due to its temporary No Export for You status, being the only numbered Final Fantasy game of the SNES generation not imported stateside, on top of being from the pre-Final Fantasy VII era. Also, whereas Japanese gamers didn't like the bigger emphasis on story that VI had, Americans did, Western critics knock down this game's lack of story and seemingly bare-bones characters (and the high random encounter rate).
Boring but Practical: Rapidfire; vetrans swear by it, but it's hard at first to understand why. You attack four times, at randomly chosen enemies, for half of your usual attack. The upsides are numerous; you can spread out attacks, you do (on average) double damage to the enemy group, and since the game rerolls damage on every attack you don't have to worry about missing or getting a lousy amount of damage (while conversely you get three extra chances at a critical). It's only at the end of the game that it becomes apparent how awesome this ability is; there is a 9999-HP damage cap for an attack that even the enemies are forced to obey; however since you are attacking four separate times you can do more than this (and with the right collection of abilities and weapons in the endgame, you will be capable of hitting that hard).
Cult Classic: While not one of the series' most popular games, it has garnered a decent following, enough to inspire a yearly charity run, FF5ForFutures, that anyone can participate in.
Faris was easily the most popular member of the main cast before Dissidia raised Bartz's profile, for being a Badass pirate and princess who actually acts like a pirate and doesn't take any crap from anyone.
Also, Galuf's Dancer costume—a shirt made of frills and orange hotpants—is a hugely popular subject for Japanese fanartists.
Fanon: Some fans take Krile's statement that Bal lacks an heir and jokes "as if" about taking the throne herself to mean that she's adopted. It's worth noting that Relm in the next game has townspeople drop clear hints that she's not Strago's blood relative, whereas nobody in Bal says that Krile was. The Ultimanias also list Relm's relationship with Strago as "raised by", while Krile's is simply "granddaughter".
Bartz/Faris is a very popular subject in Japanese fanart. Aside form Faris, however, Bartz is more commonly paired with people outside of his own game...
For example, a lot of people like to pair Bartz with Terra despite them never having spoken to one another in Dissidia, but the fact that neither one of them has an official love interest really helps matters.
Faris/Lenna is also very popular, at least in Japan. Faris' whole reason for going on the quest being Lenna, and the girls caring deeply for each other, before even it's revealed that they are sisters, to point that when Lenna is poisoned and nearly captured by Magissa, Faris goes livid, and continues trying to save her, to point that when she fall of a cliff, she just immediately climbs back, helps shipping them. Generaly, if you ignore that they're both girls and sisters, their relationship plays out quite much like a romance. The official art◊, also helps.
The most popular is Double Cast Bahamut and then Mime it. Granted, you only get Bahamut at the end of the game, but any and all fights afterwards, sans Shinryuu and Omega, become pitiful fights.
The Mime and Freelancer classes automatically get every passive ability from any class you have mastered. There are many applications for this, but the most famous is to get a Mime or Freelancer Bartz who has Dual-Wield, Rapidfire (four attacks on random targets, each at half damage), and Spellblade (charge any swords you're wielding with certain Black or White spells; only need to cast once for the whole battle). The end result is that you can attack a boss eight times in one round, for four times the damage of attacking normally. Also, each attack can be charged with the boss's elemental weakness, or just souped-up with Flare, Bio, or Drain. How powerful was this combo? Powerful enough that it became Bartz's Limit Break in Dissidia: Final Fantasy.
The GBA remake adds the Gladiator's "Finisher" ability, which, at the job's maximum level, has a 3/4 chance of either delivering a critical hit or an elemental-based hit that automatically hits For Massive Damage. Add the Knight's Doublehand ability to double your attack power and you've got a wrecking ball in a human suit.
The Chemist class, normally impressively useless due to the fact that the game doesn't actually tell you what the item combinations for Mix are. But if you do know, you can create mixes for halving an enemy's level (yes, even on a boss, in a game where level means everything), increasing your levels by 10/20, and so on. Also, halving an enemy's level makes them automatically susceptible to Level 2 Old, which drops their level further...
Also, Drain Kiss. Combine a Maiden's Kiss and a Turtle Shell (which are always dropped by an early-game enemy) and you get an attack that deals 1500+ damage at a point where every other class is struggling to deal 500.
The Return spell. If you have someone with Time Magic and just 1 measly MP, you can do the whole battle over again. Everything gets reset, including countdown timers and MP:(i.e. The spell is effectively free.), to however the battle started. This makes stealing unique rare items and figuring out any Puzzle Boss just a matter of keeping the Time Mage alive and patience.
Note that this is bugged in the North America GBA release — timers do NOT reset.
If you run away enough, the Chicken Knife becomes one of the strongest weapons in the game, with the caveat that it can randomly cause you to run away instead of attacking. Use a command that doesn't trigger special effects, like Aim or X-Strike, and you can get all of that power without worrying about running away.
The Bone Armor is very powerful armor, but makes the character harmed by healing magic. There are two ways to get around this. White Wind heals everyone a fixed number (the caster's HP) which overwrites the Bone Armor's effect. Or use Magic Sword to attach drain to your attacks.
In the Super Famicom version and PS1 port, this is done by using the Kiss of Blessing on Exdeath (Holy Water and Maiden's Kiss using the Chemist's Mix command).
It Was His Sled: Faris is a woman, and Lenna's sister. Also, Galuf dies in the most awesome death and Krile takes his place.
Magnificent Bastard: Exdeath is a very accomplished villain. He manipulates various world leaders into shattering the crystals despite still being sealed, leads the Light Warriors on several wild goose chases, gets them to actually destroy a seal that (to put it mildly) they should not have, and very nearly accomplishes his goal. Pretty impressive for an amalgamation of various evil spirits.
Memetic Badass: Galuf. When you're down to 0HP and can still fight, you know this applies.
Narm Charm: The GBA script is well-liked for not taking itself seriously. The player can also invoke this with certain job/ability combinations, such as Galuf in a Bard's frock calling on the forest animals like some kind of Disney princess... and there's nothing to prevent you from making him a Dancer in his final battle with Exdeath.
According to some, Exdeath is a laughably stupid and absurd villain because... he is a tree.
Bartz being an "Idiot Hero." He actually gets to be the Only Sane Man several times and isn't any goofier than his companions. Granted, he is The Malaproper (psychotically? really?) and Ghido spends most of his time insulting Bartz's intelligence, but that's because he was already pissed off at him. Fans (and Dissidia) tend to act like he was too doofy to survive years of wandering a monster-filled landscape.
Garula's Charge. Hits hard and inflicts the Sap status, which rapidly drains small amounts of HP. Since your characters are likely to have around 200 HP when you fight him, it's very deadlyespecially if he hits the same character twice in a row or nails multiple party members with Sap.
Shinryu's Tidal Wave, by far the most damaging attacking in the game that does over 8000 damage. Unless you're at a really high level, or possess Coral Rings (which absorb water damage, and are quite expensive even late in the game), you're dead if he uses it, and he opens up the fight with it. In essence, if you can't survive the attack, you'll never defeat Shinryu.
Puzzle Boss: However, most bosses have some elemental or status weakness, or stats exploitable by Blue Magic. If you know what you're doing, most bosses last for two rounds tops. And if you have also the Return spell...
They Just Didn't Care: Many of Faris' job costumes in the mobile release. She's supposed to be Bifauxnen, and the original gives her fairly androgynous (or at least less feminine) outfits most of the time. The new sprites make her as busty as Lenna except for the few jobs where her chest is obscured with a shawl or tabard. The trailer even shows her job artwork, where her build is obviously patterned off of Bartz and Galuf's, but it's not reflected in the game.
True Art Is Angsty: Most reviews that praise the game still make a point of calling the story and characters flat, even though they do have quite distinctive personalities and Character Development. That's what happens when the previous and subsequent games have casts of 10+ people with world-affecting existential crises and/or Love Hurts problems.
The Woobie: Krile. Unlike the main cast, who are at least eighteen, she's a kid who's been thrust into fighting a world-destroying entity who killed her only living family member right in front of her eyes. Her reaction to having to take Galuf's place is heartbreaking, and the fact that she's The Cutie just makes it worse—in spite of all that, she manages to perfectly embody the element of Earth and Hope.
Woolseyism: Nobody really complained when the main character's name was quietly switched from Butz to Bartz for the U.S. localization. Many of the lines in the Game Boy Advance remake also qualify for making the script more fun to read compared to the rather bland translation of the PlayStation version.