People often talk about Final Fantasy VII as their personal breakthrough game that got them into RPGs. If you were a kid in the early '90s, however, odds are your version of that same experience was Final Fantasy IV (though you would have known it as II if you weren't Japanese). It looks exceptionally primitive now, but at the time it was an amazing advance in color, storytelling, battle engine and especially soundtrack as compared to even the other 16-bit systems.
So this is one of those nostalgia games beloved to people of a certain age, but probably seen as mediocre and boring to anyone who didn't play it within a few years of its original release. Of course, it was never going to get a full-blown remake with a budget of tens of millions of dollars to try to make it fresh for the Call of Doody Generation, but in 2009 Square did lay out a more modest amount to do it up in polygons on the DS, using their previous Final Fantasy III remake engine as a base. This put it more on par with the visual and gameplay style of the initial PlayStation generation (FF VII - IX), something at least more likely to be familiar and acceptable to younger gamers.
So it's got polygons, it's got voice-acted cutscenes with the usual VA suspects like Jennifer Hale and Lance Bass, it's got a semi-refined soundtrack that subs in some pieces from the Celtic Moon album, and it's got a flowery new "period-ish" script to replace Ted Woolsey's clumsily charming but also sometimes nonsensical original localization. And it's got a lower score than the original game, at least from me, because I don't think all this extra weight actually improves the game in any meaningful way, and in fact it's a little worse in some measures -- it's slower, it's more bloated, the script has gone from charmingly inept to cringey fanfic, and gameplay fuddling by the new dev team has thrown the original balance way off at points.
One nice thing you can say about it, however, is that these are all just added layers on top of a core that is actually very faithful to the original game. It's essentially just a really big "grade up" attempt, with the structure of the underlying game not changed all that much. That extends to the character designs too, in a big way. Though the polygons are muddy and not particularly appealing, you can see that the art team made an impressive effort to really replicate the original artist designs in 3D form, down to individual monsters and supporting villains like the Four Fiends. Well, except for Rosa's stripperific new outfit, I guess.
New gameplay stuff unique to this one is pretty much limited to the Augment system, which is basically just the ability to equip characters with other characters' abilities. Each character usually hands their key ability (i.e. Bardsong for Edward) off to you as an augment when they leave for good, plus there's a few new abilities hidden around and about. There's also apparently a couple of hidden new superbosses, but I couldn't be stuffed to get to them. This version does not include the After Years or the other new content that the 2D PSP remake had.
The only other structural change they made was to fiddle with battles a bit, and this is another area where the game becomes inferior to the SNES originals. You'll see much made about the "increased difficulty" of this version versus even the original Japanese release, but that only really comes into play very late in the game, and it's an absolutely ridiculous and sudden spike even for veteran players. Battle experience has been majorly increased in this version (while gil has been majorly decreased), so for most of the game you inadvertently level so fast you still truck all the common enemies. The only significant earlier-stage difficulty increase is that certain bosses are given cheap new abilities, mostly auto-counters, that throw off the balance of the original design and turn the fight either more into a luck-based shitfest, or a situation where only one attack type really works and you have to sit around with your thumb up your ass for a bunch of wasted turns until that lone person can do some damage. The advanced difficulty only really begins from the first moon trip onward, where even for what would be a terribly overleveled party for the original version of game, enemies still start getting 2-3 turns to yours (and often still get two when Slowed) and just hit way too damn hard and have too many shit status effects attached to their blows along with garbage auto-counters. This design fiddling fucked the late-stage bosses too, from the Giant of Bab-il onward, by trying too hard to make them Super Hardcurrrrr and throwing the whole balance right off the rails.
Perhaps even worse is that the game has lost a great deal of its charm. The original goofball English translation was a big part of the fun, and while I'll concede it made the plot confusing at times and there was room for some more clarity, this swings way too hard in the other direction of being overly self-serious and tryhard. A Vader-like "Nooooo" by Cecil in Myst early on, complete with camera pulling upward to the heavens, lets you know early what you are in for. The script also does that thing where it seems like three different groups were working on it and each thought it was supposed to be written in a different period -- one present-day English, one Game of Thrones and one Pirates of the Caribbean -- so it just kind of keeps randomly drifting between styles. FFIV works best as a simple monomyth with relatively little talky-talky; melodramatic cinematics and flowery dialogue detract from its punch, making it outright farcical at times.
The final strike against it is the speed -- the game plays out at an acceptable 30 FPS until you get into battle, at which time it drops to a locked 15 FPS. Not only is it noticably laggy, you have the issue of commands getting cut off unexpectedly by Summon animations and the command menu disappearing and "rebooting" if an enemy you happen to have the cursor on dies before you issue a command. This might not seem like a big deal at first but it wears over the course of a 30+ hour game, especially as enemies get superfast and cheap in the final segments.
In the end, it's a bunch of polygons for nothin'. I'd reccomend any of the SNES versions over this, even U.S. Easytype with the wonky translation, but the version of choice is really the PSP port
with the enhanced sprites and pile of new content. Unfortunately, that one's stuck on the PSP only, while this is the one they chose to make available on mobile and PC in all its locked-at-15-FPS glory. It's still an OK way to play the game, I suppose, if you can get it on the cheap, but literally any other option is better.