Yeah, for all that the GBA port added to the original version, the really tinny GBA speakers and washed out pallet really did no favors to it.
And really, outside of the new translation the additions were mostly hit or miss. The biggest mechanical fix was making Evade actually work instead of just reading from M Evade (of course being separate stats to begin with was pretty damn unnecessary), with the second biggest(/other?) change being the removal of the Invis/Doom trick (but not actually fixing the Clear/Invisible glitch, leaving the near-literal minefield of Relm's Sketch intact, among other things), while the new spells really didn't add anything (by the time you got Flood it was most likely already outdated, Valor only affects the first hit of a given attack making it useless, and Gravija only shows up after trashing the bonus dungeon boss making it the game's new Sword of Infinity+1), though the new Espers did do a bit more but are still pretty useless (Leviathan is probably the most useful since the fight against it can be used to teach Mog Water Rondo in the WoR which is otherwise impossible to learn by then, Gilgamesh's gimmick isn't too bad for when you get him, Diabolos who again shows up way too fucking late to matter at all, and Cactuar who sports a useless gimmick and the Speed +2 stat boost which still doesn't matter since the ATB's calculation still has almost no use for the Speed stat).
The aforementioned Bonus Dungeon is a mess in design since it cobbles together dungeon assets used throughout the game almost haphazardly, making the dungeon ridiculously long and navigation a bitch, making the multiple parties gimmick really fucking annoying (by mandating a very specific order of actions that if done incorrectly could very well force you to have to warp all the way back to start), the bosses' gimmicks got very stupid at times (having to MP death the Earth Dragon mk2 in particular), the enemies were mostly blobs of HP and didn't do anything new or unique, and the prizes were just Superweapons+ mk2 (which didn't matter for most of your characters since you could farm Ragnaroks, Illuminas/Lightbringers, and Atma/Ultima Weapons from Kefka in this version (which in turn made the choice for the Ragnarok Esper or Sword a no-brainier) and they're still better than anything this dungeon gives you).
And then there's the other area which is more of a enemy rush rather than a proper dungeon, is stupidly long, and has gimmicky bullshit that can easily wipe you on the later floors (and more gimmicky bullshit like interspersing enemies that you can steal Gemboxes/Soul of Thasmas, Economizers/Celestriads, and Offerings/Master's Scrolls from but do shit like spam Ultimas or insta kills at you).
All this of course, and the rest of the game's code is still a literal clusterfuck of bad design choices, trivial challenge, and game breaking bugs.