Alternate Character Interpretation: There are those who believe that Marche is really the villain and that he is essentially killing off a world full of people and stripping his family and friends of their hearts' desires in a selfish wish to go home. While the sequel more or less confirms that things worked out pretty well for everyone, it is true that the game isn't great about arguing against this point of view. Added on that since his actions involve forcibly changing the world explicitly against the will of it's citizens, it's easy to say that he behaves like a villain sometimes regardless of if he's ultimately right or wrong.
Author's Saving Throw: The Radio Edition addresses Marche's motivations and the nature of Ivalice far more in order to avoid the issues players had with the game. And the sequel confirms that, whatever else he did, Marche's actions in the story don't amount to genocide.
Broken Base: The game itself heavily divided fans of the Tactics series, mostly due to the new gameplay direction and the story.
Designated Hero: Just for the record, there are a lot of fans who consider Marche a Villain Protagonist because he decides on his own (and fairly quickly) to destroy Ivalice and restore the real world, without trying to convince his friends or looking for a way other than destruction, although the story paints Ivalice as a Lotus-Eater Machine and gives the Aesop that dealing with your problems is better than hiding from them.
Draco in Leather Pants: Mewt Randell and the Li-Grim. Neither is necessarily evil, but they qualify in a sense due to people seeing them as more sympathetic as they are, especially considering that Mewt is mainly selfish and willing to make the laws harsher against his subjects' wishes on a whim.
Esoteric Happy Ending: While they lost what they had in Ivalice, and while at the very least they will never see their friends there again (subsequent games have confirmed that they didn't quite destroy the place), Marche and company have at least learned to face up to their problems and work towards self-improvement... even though that means Doned can't walk.
Fridge Horror: The scene where the real world transforms into Ivalice includes random bystanders turning into monsters. That's right, the main characters might be better off in this wonderful fantasy world, but there are plenty of other people who now exist to be beaten up over and over until they either die in a Jagd or are captured and sold into slavery. It might actually help justify Marche's actions.
Note also that "Lost Souls" you fight the first time you save Professor Auggie have the same names as the bullies who picked on Mewt in the beginning . . .
Also, the "Fire! Fire!" mission, involving the player having to stop a group of Bombs from burning down a neighborhood, with the implication that if you fail, the judge watching over the fight won't do a damn thing to stop the arsonists.
As mentioned in the Jerkass Woobie section... Ritz's reason for wanting to stay is her white hair. That she gets bullied for. Given that Kids Are Cruel, there's a great chance that she was bullied into having a mental breakdown.
Game Breaker: Concentrate breaks most skills clean in half, since low accuracy is what keeps them balanced, and three races can learn it. Double Sword is also fairly ridiculous, but that's Human-only. Doublecast is terrifying when you consider that it works on Summoner abilities - yes, including Madeen.
The only thing worse than the above skills is using them with other classes' moves. A ninja with two swords? Unnerving. A paladin wielding two swords, both of which are insanely powerful? Scary. A paladin wielding two of the aformentioned swords and toting Ultima Shot, arguably the most powerful human spell in the game? Freaking terrifying.
Ultima Blow is unnecessary if you get Sonic Boom, which deals normal damage to multiple enemies at a nice range. Paladins are also capable of equipping a combination of equipment - Nagrarok, Sequence, Peytral, and Ninja Tabi - that allows them to have a total movement range of eight squares, over twice what they ordinarily have and more than enough to cover half a map by themselves. In combination, this gives them the same attack range as a Gunner.
Also, equipping a Bangaa Dragoon (highest attack base stat and growth in the game) with the Gladiator's Ultima Sword (triple attck damage) and the Templar's Weapon Atk+ (guess) can kill literally anything. Yes, even the Stone Wall Toughskins. Even the 999 defense Flans. It is even possible to one-shot the final boss with this.
Raising a Gunner as a Mog Knight gives you access to Ultima Charge from across the screen. If it's not possible to scrounge up the MP for that, you can also spam Stopshot or Charmshot, which disable any enemies they don't outright kill. Add Counter and you have a killing machine.
Steal: Ability, intended as a late game accelerator pedal, can be acquired with a couple of hours of cheesing, turning it into a Disc One Nuke for both Humans and Moogles. This frees munchkins from having to waste time learning abilities and lets them move straight into stat optimization.
HP<->MP is generally not terribly useful, but it *does* break any Duel Boss situation clean in half; as long as your speed is high enough to get a turn for every turn your opponent receives, it will block all damage, because you regenerate MP every turn and the reaction skill will nullify all damage if you're not at 0 MP when it fires.
Combine it with Immunity, which makes you immune to poison, and you will be outright invincible when you face Llendar in the palace.
Make 3-4 Viera Assassins with Sniper multiclass. First round, everyone go invisible. Second round, everyone appear behind target and use either Last Breath or Ultima. Now you have your very own Viera Death Squad.
Goddamned Bats: Sprites/Titanias (particularly those with White Wind), enemy Gunners or Illusionists (who can hit you from far away), and anything equipped with Damage > MP. The latter ability results in damage reducing the target's MP instead of HP, and, worst of all, as long as the target has any MP, they will not lose HP.
On the Les Yay side, we have Ritz and Shara who have grown very close to each other by the time Ritz tearfully throws herself into Shara's arms.
Jerkass Woobie: Doned does some pretty fucked up things towards his own brother, including destroying a present Marche needed to see Mewt, but at the same time, the wish he gets in the fantasy Ivalice (the ability to walk and robust health) is rather big compared to the others. Kinda understandable as to why he loathes the idea of going back.
Ritz to a lesser extent, mostly during the time frame when Marche is on the lam. Her reason for not going back is because she hates her albino hair. Sure, other kids seem to dislike her because she's outspoken too, which could also be something, but it's outright stated that her wanting to stay is because of her hair.
The be fair, Ritz hates her white hair because she's constantly bullied about it. It's possible that being bullied enough has driven her to the point where she mentally broke down, which would justify her desire to not lose her now naturally pink hair. However, being with Shara and the other Vierra gave her enough confidence about her white hair and ultimately reached the point where she stopped dyeing it after returning from Ivalice.
Narm: Ritz revealing why she's refusing to help Marche... because of her hair color. Bully-magnet or not, differing cultural standards or not, complext over it or not, that's one of the silliest possible reasons she could have put out for what the Gran Grimoire gave her. Hell, Shara seems to be as confused as the player!
Ritz does go into further detail on this when speaking with Shara in private: she hates her hair so much because her mother is always sad when she helps Ritz dye it, which is why Ritz hates her hair so much, the bullying situation notwithstanding. Shara points out that it's more than likely the other way around; Ritz's mother is sad because of Ritz's contempt for her hair.
Ron the Death Eater: Marche is commonly accused of many things, from selfish disregard for his friends to a desire to commit genocide, that ignore his honest attempts to get them to face their problems and his frequent moral conflict over his course of action, regardless of the rightness or wrongness of his actions.
Scrappy Mechanic: The law system can really piss people off. Though canny players can turn it to their advantage sometimes (notably, waiting for Charm to be illegal makes the second Totema fight a complete joke), the presence of enemies with red-card immunity puts a sour taste in everyone's collective mouth.
Vindicated by History: As of 2016 with its Virtual Console release on the Wii U, there have been some people who have pointed out that while the plot concept is adolescent (it was mentioned by several magazines it was like The Neverending Story), it actually has a lot of mature themes in it that a lot of people didn't notice in 2003 such as the effects of divorce on children, the stages of grief with the death of a loved one, bullying and the desire to retreat into fantasy as a coping mechanism, etc.
Viewer Gender Confusion: Marche, in his Illusionist costume. More or less invoked with just about all of the human characters, especially the generics - for the most part they're all androgynous enough to be interpreted as either male or female. You'd think FF fans would be used to androgyny by now.
The Woobie: Doned. Despite that he acts like such a little shit, he actually had the most reasonable wish out of all the four (which was to be able to walk again). And in the ending, he goes back to being an Ill Boy in a wheelchair. Despite getting friends, come on...
Crosses over with Jerkass Woobie, and it's a similar deal with Mewt - on the one hand, he seriously lacks confidence and self-esteem and misses his mother; on the other, he prioritizes his own comfort and feelings over that of others. Both characters (and even Ritz, to a degree) have understandable desires, but go about them with disregard for anyone who disagrees.