Yes, hands down this is the best version of FF4 released on any platform. It has the Wonderswan Color version graphics (but even improved upon that, especially for battle backgrounds.. but they are definately a step above the SNES graphics). And I believe the superior translation of the PSX version (though I could be wrong, I havn't compared the two so maybe they are different. But it's def. not the SNES translation). The Zeromus battle has massive slowdown though, so watch out for that. I've also heard it's slightly easier than the Japanese version (and I suppose the PSX version). But it wasn't bad. It's def. not as easy as the SNES one.
Minor Spoilers ahead:
But really what impresses me about this version, and I bet you are not that far yet, is the extra content. It's extremely freaking fun. First off you get to use Yang, Cid, Palom, Porom and Edward (who still sucks horrible ass) again. There is a brand new dungeon just to give them new lvl 50+ gear which is fun. It's nothing extremely special but some of the bosses there provide a decent challenge.
But the real improvement is the Lunar Ruins dungeon after you beat the game. The basic idea behind this is that Square has something like 100-150 pre-generated rooms. The dungeon is 50 levels and picks from these rooms somewhat at random (it seems to be more like, every three floors, there is a set of maybe 6-8 rooms those three floors can be). So that alone adds some replayability because most of those floors are really unique. Some are basic battle floors, but a lot of them are real puzzles. Some examples: One involves finding a book in a huge library for a guy. You can talk to people in the library for hints on its location. Another is sort of like a personality quiz and at the end you get rated as a class (i.e. "You are a Paladin" or "You are a Monk"😉 and you get different items based on that. Another is a floor where there is a bad-ass dragon that wanders it. You can avoid him, but if you fight him he's probably the hardest boss in the game (yes, harder than Zeromus.. he is quite insane). Another is simply a fountain with Sylphs that heal your party to full health and give you a Mexalixer. So it's pretty random like that. And there is good loot to be had on most of the floors too.
But then about every 3-4 floors there is a floor with a "Trial door", of which there is one for each character (actually, Palom and Porom share a door). Each is a really unique challenge which must be faced alone with only that character. Some of them are easy. For example, Cecil's is a bunch of morality trials where he has to not steal a chest from an old man who fell asleep, or stop a robber who is stealing, etc. (Incidentally, he gets an insanely bad-ass sword from this, it's fucking crazy and the only weapon that can really exceed the 9999 damage barrier because it sometimes casts Holy on hit). Rosa's is a crazy hard one where she must heal everyone in a town that has been decimated within a time limit (hardest part is they don't tell you that time limit). Kain's is a wierd murder mystery thing which isn't bad except you have to face Lunar Behemut after that who is a freaking PAIN IN THE ASS. If you don't time everything right he can wipe Kain (only person you get to use) with one hit. And that's not so bad except you have to repeat the whole trial again which takes around 15 minutes to do -_- If you do that one, bring a damn Lunar Curtain. God I hate Megaflare. Cid's is a version of Crazy Taxi.. etc.
And at the end of each person's trial they get an item which for most of them in some way enhances one of their class abilities. For example, for Palom and Porom it changes Twin to sometimes cast Double Meteor (which is worthless because it does 9999 regardless, which is exactly what regular Meteor does minus the 2 minute casting time). Rosa get a ring that changes Pray to the very awesome Miracle which from what I can tell randomly switches between Cure, Cura and Curaga for the whole party (but ususally the last two) and sometimes casts Esuna on everyone. Pretty bad-ass. Oh, and it never fails like Pray. Kain gets a ring that changes Jump into Double Jump which basically hits twice on a Jump. Not bad. Cecil and Cid both get awesome weapons. Rydia gets a ring that enhances her Summons damage and changes Mist Dragon summon to cast Blink on the entire party (very useful, but also a good way to witness the slowdown that is the GBA processor.. if you do this on the Zeromus battle.. umm yeah, good luck with your 2 fps 😊). Edge gets the oh-so-predictable change of Steal to Mug (I forget the exact name they used, it wasn't Mug but it's the same thing.. steal and attack at the same time). etc
Then there is a final boss who is the USA version of Zeromus (well the toned-down USA graphics.. though really what was wrong with the original graphics? Was he too "gross" looking?). He's a bit harder than Zeromus but not much, and he doesn't have a first form (that you can steal Dark Matter from). So his Big Bang (is that the right spell?) does a bit more damage. He's totally pointless though. Once you kill him you get nothing. No extra ending, no special items. Nothin. So it's a bit annoying.
But yeah, it's pretty varied which is cool. It's probably some of the most interesting content in the game and really I can't wait to see what they do with Final Fantasy VI Advance. They could do some bad-ass stuff with that. I wouldn't mind seeing them tie up some plot holes that always seem to turn into internet rumors (i.e. Siegfred stealing that chest.. that is so out of the blue and pointless.. Or a rumor that there is a device in the capital city - I forget the name - that can revive the dead.. oh what fun "Let's bring back Gen. Leo!" rumors that brought, etc). Would also be a great way to really data-cise the game like they did with the Bestiary. Like, a list of all the monsters you have Lept on the Veldt. Or if a monster uses a Blue Magic ability (excuse me... "Lore" ability -_-), listing that in their Bestiary entry. etc.