Kids these days have a lot of options when it comes to Final Fantasy 4, and most of them aren't going to choose any of them. They're too busy arguing the merits of Cloud v.s. Zack and jerking it to Aeris-Red XIII pr0n.
Back in MY day, however, we had Final Fantasy 2 (4 U.S. Easytype whatever) and that was all we got. The Internet Tubes had not been airlifted into place yet and knowledge of the Japanese gaming scene was restricted to the occasional lazily written article stuffed into the back pages of an EGM somewhere.
It had a lovably goofy Engrish transration that spawned many good lines and good times, but we didn't know that we were missing out on such plot bombshells as THE FACT THAT CECIL AND ROSA ARE FUCKING OMG. Plus that one chick in Baron shows her flat pixely swimsuit clad body, Rosa almost gets annihalated by giant guillotine instead of giant steel ball, and there's swearing. But, more importantly, a whole set of battle abilities were dummied out of the game for reasons I still don't even understand. Also, although certain battles were challenging, it really was pretty easy overall.
Nowadays, you have some options.
You can play the game in all its original glory by downloading a ROM of the Japanese version, a copy of ZSnes, and the thorough translation by J2E (I don't link to any of this shit, I assume you know where Google is). Cecil can use Dark Wave for the first couple hours of gameplay, Edward can burn through all your potions doing Medicine, Tellah can randomly cast the wrong elemental spell on enemies at inopportune moments, etc. You also get to beat your head against the wall in frustrating boss battles, such as the Death Wall in the Sealed Cave where the designers seem to have applied a bucket or two of chicken grease to the floor.
There are also two sort of weird, aberrant versions that are hard to find. The first is the Playstation port, found on the Final Fantasy Chronicles collection or whatever that also has FF5 and FF6. Oh, in Japan, that is. For the Gaijin version, they totally wiped out FF4 and instead replaced it with some random playlist of 20 of some Squaresoft janitor's favorite FF6 songs. Nice trade-off, Square! Of course, they did this because they wanted to later sell it to you in another Playstation pack-in version (this time smushed together with Chrono Trigger). In either case, these are both eBay collector hoarder things that are expensive and hard to find and even if you do get one now, you have to put up with crazy load times. They also added some cinemas, but they're very short and they look like shit (seriously, save your money and watch them at Youtube if you absolutely have to see them -- there's like maybe 3 minutes worth total over the course of the whole game).
There's also the Wonderswan port, but since nobody has a Wonderswan, nobody cares about that.
Most recently, there's been Final Fantasy 4 Advance for the GBA. This is sort of a modified port of the Wonderswan version, so if you're curious about it you can get that experience here. What you get in FF4 Advance is the script and graphical censorship of the U.S. FF2 combined with an even lower difficulty level. On the flip side, the extra character abilities are retained, and the graphics have been given a touch-up. The dealmaker for most Final Fantasy 4 fans is that there is dun dun dun NEW CONTENT - specifically two new dungeons, and the ability to change characters from amongst the other living party members after the Bab-Il Giant is destroyed.
What they've chosen to censor in this version is interesting - Holy is Holy again instead of White, Tower of Wishes is restored to Tower of Prayers and everyone does a lot of prayin' there, Rosa
still nearly gets chopped into messes by guillotine and not giant pinball. However, that dancer in Baron doesn't strip to her pixelicious bikini, monsters with boob cleavage have had it mysteriously removed, and all vague references to characters being in sexual relationships (Rosa and Cecil, Kain and Valvalis) have been whitewashed. The secret Developers Room in the dwarven underworld has been restored, but the Porno Mag is conspicuously absent. So, taking measure of the cultural landscape by using FF4 Advance's example, violence is still OK and religion is no longer sacred and unmentionable, but sex is still awful and nasty. Righto, Square and Nintendo, thanks for the update!
This seems to be by far the easiest version of FF4, even easier than good old Easytype. I've seen some people around on the internets claiming that this is due to the fact that those of us playing it mostly have been through the game before and therefore are just really good at it. Well, let me see .... I've played through the original American FF2 two or three times from start to finish, and went through the Japanese FF4 once when the J2E translation came out. So my experience certainly may be a factor - I knew exacly what to do in each major battle. However, all of these run-throughs have burned certain things into my brain, and I don't remember most of the bosses taking so few hits to go down. I also recall them attacking a whole lot more often, and doing more damage. Demon Wall is a good yardstick - he only managed to lurch forward 3 steps before I wiped him out in this version. I also recall having to grind to get through a couple of battles in Easytype - the Calcobrenas and Golbez for one - that I walked right through in this one. I'm fairly confident that, at the very least, Boss HP and speed has been toned down even from the Easytype version, and that your party's strength has been cranked up a considerable bit. At the very least I know it didn't take me a meager 15 hours to complete any previous version of the game, all sub-quests included - and I certainly wasn't hustlin' either.
There are some battle glitches in the U.S. release that you would think would make the battles harder, but they're so toned down that they really don't. For example, the menus scroll slow as molasses when you're looking for an item or spell, and button presses often don't register on the first try. There's also a bit of lag when there's a lot going on, most notably during the last battle with it's crazy parallax scrolling background. It's a bit of an annoyance, but was apparently fixed for the European release.
As far as the graphics go, there's new character portraits that actually look pretty nice. Apparently the battle backgrounds have been touched up, but I really didn't notice much of a difference. The music hasn't really been messed with for the most part, but purists will note some instrument changes and such to accommodate the GBA's sound chip that might sound a little off. I thought Golbez's theme sounded hella more menacing and echoey in this version, though.
This brings us to the main point of interest for this re-release - the new stuff.
The main thing is that you can now change characters at the Tower of Prayers/Wishes, at any point after the Bab-Il Giant has been completed. You get everyone but Tellah, who's dead for reals, and FuSoYa, who's off Ramboing it through the final dungeon with Golbez. They're somewhat interesting to play as, and fairly well balanced with the other characters as they level, but don't offer a whole lot of compelling reasons to play as other than novelty. Cid and Yang are offensive beasts with high HP but have crap defense, Palom and Porom are basically Rosa and Rydia again (minus the summon ability), and Edward is almost completely useless unless you employ the Psycho Edward glitch. There's also an issue with getting them a full suite of equipment that is on the level of what the regular party members have - though some is provided, it becomes a challenge to get a full set for all of them that keeps their defense competitive.
A new cave also opens up at the base of Mt. Ordeals, which is basically there to get Ultimate Weapons into the hands of the five newbies. It's a rather short and easy eight-level dungeon populated with enemies mostly from the Lunar Underground, and the five boss battles by which you secure the weapons feature palette-swapped versions of common enemies that have had their stats kicked up and been given new spells/abilities.
The Lunar Ruins are actually a bit more interesting - first of all the design is just very weird and trippy, and then you have the Trials for each character which have both new enemies (in terms of entirely new artwork) and also some logic/timing puzzles (basic stuff, within the framework of the game's engine) sprinkled throughout them. Some of them just have a series of fights, but for example Cecil gets a randomized series of moral decisions to make, Kain has a murder mystery and Cid has some Crazy Taxi-like airship delivery mission on the overworld map. There's also the optional superbosses Brachioraidos and Zeromus EX if you are into that sort of thing. This all doesn't open up until you beat the game once, however, and then only characters that you have defeated Zeromus with can enter, so you actually have to beat the game about three times to get everyone eligible for it (the game now has a sort of New Game Plus feature to facilitate this).
Oh, and there's an ongoing Bestiary in the style of many other Square games, and you get a music player unlocked when you finish the game.
It's hard to say that this is the definitive version of FF4, because other versions still have small advantages on it. Mostly the issues with this one are that some of the music sounds a bit inferior and that the difficulty has probably been lowered a little too much for most people's tastes, and that some of the censorship issues are present. It's by far the most affordable and accessible version of the game right now though, if you want to own an actual physical copy of it, and the flaws really are pretty minor and ignorable. And hey, it's portable, you've got the new content, and the translation is cleaned up notably.
Japanese TV Commercial with random sexy bedhead Rosa
Golbez Battle - one of my favorites
Dr. Lugae Battle - hehe another one of my favorites
FF4 Theme of Love played at Tour De Japon
Conan is Zeromus!