I'm going to start with the core gameplay, as it was back when this game was orginally released. You can't deny this was a very ambitious system. 23 Classes, each with their own strengths and weaknesses. Their own equipment restrictions, their own abilities. This game is often compared to Dragon Quest III, in that you really got to mold your party how you wanted it. This game does many things that DQ III did not, however. It forced you to learn the class system, introducing new more powerful jobs as the game went on. Some bosses were very weak to certain classes, and some classes might be particularly hindered at certain points in the game. Also, there are the mini areas where physical attacks are nearly useless. This is something I wish more games with job systems did. Encourage magic use in a sense greater than bonus damage if you know the bestiary very well, now there were some ways around it, such as using the Dark Knight ability Souleater, but still the effort was there. The actual job level system could've been thought out better. Its done through a point system where you accumulate points by basically being that job for a certain number of battle rounds. It could be kind of taken advantage of through defending for multiple rounds and kind of just made the process more tedious than in needed to be.
Now, to speak about the changes when they brought this game to the US. Unfortunately, there is no official version in the US that uses the original engine. When they brought it over, they decided to give the game a completely new look using a new 3D engine for the environments and fighters. This gives all the PCs and NPCs more animation in battle sequences, the backgrounds and dungeons are more fleshed out and certainly prettier and really turns the game into utter poo. There are alot of limitations from this engine which really hurt things. Firstly, it limits the number of monsters per encounter to 3. While this doesn't kill gameplay, it certainly limits some of the things they can do in random encounters. Also, the battles are slow as molasses in normal mode. You can press select to put the battle in Auto mode which speeds things up to a more normal pace, however, if you're not careful this will automatically input commands for you, and for reasons I'll explain in a minute this can get you in trouble.
The boss fights in this game a re a bit ridiculous. They are massively more difficult than any other encounters in their area, and this is due to the fact they get multiple attacks in a round. This wouldn't be so bad, however, they get all their attacks successively, which means if they gang up on one member you have no chance to save them from dying. This means, you really have to carefully think out each round in a boss fight, but if you use the Auto battle function liberally because you can't stand the slow pace of battle, you will sometimes accidentally do the wrong command and once you start losing members its pretty much unrecoverable. It's a real problem.
As for the new content, lets start with Mognet. When the game was originally released on the DS, you had to use friend codes, and after sending messages to people over friend codes it unlocked messages from in game characters, which unlocked sidequests. Which, if you didn't know anyone else who had the game, really made things annoying, because you couldn't do the sidequests. Thankfully, in the PSP version, they seem to have in-game locks on the NPC messages, though what they EXACTLY are no one seems to know. The last one from Alus which unlocks the ??? Cave is especially cryptic since it seems to involve being at a certain point in the story as well as completing a certain amount of the bestiary and opening a certain amount of treasure chests and completing all other sidequests. As for the acutal sidequests, the Legendary Blacksmith gives you some incentive for actually maxing out job levels, and the new weapons and such you get certainly make some of the earlier classes usable in the end game, which is always a good thing. The ??? cave is acutally a really awesome thing. Firstly, it makes the Onion Knight accessable by giving you an area with lots of high level dragons to fight. Secondly it makes them accessable by having all the monsters give a chance to drop the ultimate equipment, the Onion equipment. Thirdly, it gives you a boss which is actually a slight challenge for high level Onion Knights! Of course, I found it more fun to try to defeat it much earlier and with a strategic group setup. It took me many many tries, but was oh so satisfying when I finally was able to take him down.
Finally, I'd like to talk about story, graphics, and music. Orginally, FF III was a throwback to the original in the fact that it starred 4 nameless characters. The DS/PSP update changed this and actually gave the characters names, and a small amount of backstory, as well as having some of the other story characters become close with certain characters in your party. Then, they continue this by only allowing those characters to receive their Mognet messages. Very cute idea, not completely necessary, but it works. The story itself is really the beginning of what would be the template for the next few Final Fantasies... Multiple overworlds, big villain, beat him to find the REAL big villain. Tried, true, and works. The rest is really pretty simple, it got formulaic after a while, Find town, solve town's problem, proceed to next town. Yep. that pretty much covers it. As for the graphics, like I said before, the upgraded engine certainly makes things nice to look at. My favorite is some of the caves that had an effect that made it look like you were spiralling downwards. Pretty cool. All the backgrounds were really nice, and again the animation of the pcs and monsters is a big upgrade. Its too bad they couldn't fit more than 3 on the screen at a time. The music, I feel is a step down from the first couple games. There are very few truly memorable tracks in this game. As I'm typing, maybe only 1 or 2 come to mind, and the newer versions don't resonate as well. The original Cave of Ur track with its vibrato was pretty cool, in this version it was smoothed out, and really doesn't have the same effect.
So, in conclusion, this really may be my least favorite out of all the games I play in this run. I think the improvements made in the re-releases of I and II push them higher, while the new 3d engine for III doesn't help it any.