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.
Refia is arguably the most popular of the four DS protagonists, only rivaled by Luneth.
Demonic Spiders: Every enemy that splits when it takes physical damage from a non-katana. They can quickly prove overwhelming if you're not prepared for them.
These foes are easier in the DS version, in which these enemies only split on their turns if they're hit with a non-katana instead of immediately after they're hit, and only three of them can be out at a time, making it easier to kill them with a multi-target spell, or with the Dark Knight's Souleater.
The Geomancer's Terrain skill, also in the remake. At high Job Levels it does damage nearly equal to (or in some cases, greater) than a Summoner and can be used every single turn for free. Even early on it is a great alternative to using a Black Mage, since even at low Job Levels it usually outperforms the second-tier elemental spells. The only downside is that the attack chosen is random (and a few of them are instant-death attacks, which means a wasted turn on bosses), but nearly all of them do the same amount of damage to most enemies. The exception is the rare attack Shadowflare, which will do thousands of damage even at Job Level 1 and will reach 9999 later on. Three Geomancers plus a White Mage/Devout can rip through most of the game with incredible ease, especially if you grind Job Levels early on.
Notably, the chance for Shadowflare increases drastically in the Bonus Dungeon Eureka, which contains the best weapons in the game.
Good Bad Bugs: A bug involving the inventory in the Famicom version allowed the player to acquire the very powerful Onion Equipment at the start of the game. (It takes a huge amount of time to set up, however.) Another one in the DS version allows players to duplicate any consumable item in the game, up to and including the rare and precious Phoenix Downs.
It's odd, since in Japan, it was voted the fourth most popular FF game (after X, VII, and IV). However Word of God said that Final Fantasy III involved an ungodly amount of complex game code, all designed to push the Famicon to the breaking point in terms of graphics and content with regards to the job class skills. And that the programers at Square basically declared that it would take too much time and too much money to decipher the game code and upgrade it for reissuing. It was not until nearly two decades later, when Square was back on good terms with Nintendo and needed something that they could release for the Nintendo DS, that they finally put aside the cash for their programmers to effectively rebuild FF3 from the ground up for a US release.
Scrappy Mechanic: The adjustment period when changing jobs. It varies in length; as low as two for transitions between jobs of like specialty, but up to ten if you're switching from a magic-oriented to a physical-oriented job, during which time the character has lowered stats. Combined with the fact that jobs have levels independent of character levels, it rather encourages players to lock into a handful of preferred jobs rather than sink time into experimentation.
Seinfeld Is Unfunny: The class system this game introduced to the series has been done better in so many other games by the time it was finally localized it doesn't reach the standards of even V. Never the less, several gamers found it to be a refreshing break from the immense complexity of other titles in the series.