Well, this has been one of the highlights of the summer for me so far.
I played the original way back in 2006; it was a funny time in my life, to the point that the place I lived didn't have a TV. I literally bought the special edition PS2 slim (sold on when I moved back to the UK, sadly) and brought it to the local Internet cafe to connect to their displays. Obviously I eventually got a telly and played through most of the game in about 40 hours or so (I literally checked this today on my old PS2!) until I just stopped. I think it was a combination of the game speed, the fact I wasn't really understanding what happened that well due to my more limited Japanese abilities and the fact I'd gotten an Xbox 360 at that point and was being wowed by stuff like Rainbow Six Vegas, Fifa 07 and eventually Blue Dragon.
Coming back to it has been a bit of a revelation. I'd done weird conversion stuff to my saves to try and make them work on a Western copy but by the time I did that it was already too late. This, though, may as well be a semi-sequel. It takes the addition of a job system from the Japanese rerelease and expands upon it; the original release had everyone advance along the same licence board, the PS2 release giving job-based boards for characters to select, and now after about 10 hours I have unlocked a second board for everyone. That's 12 jobs across 6 characters. I used a guide on GameFAQs that someone wrote up for a 'lore appropriate' way to divvy them out and the experience has been satisfying and brings out more of the characters. They give the heavy two-hander Breaker role to Ashe which really suits her character as she's a lot angrier than I remember her being.
Speaking of memory of the game, I am finding it much easier to follow simply because I understand the language a lot better. I guess playing through the entire Trails series will prepare you for political intrigue and double crossing pretty well! 12 was the first one I'd attempted in Japanese and that definitely didn't help.
As a port, it seems solid enough. Loading times are noticeable but not too long, graphics look alright (though I wish I could turn off the framebuffer blur) and menus are more responsive. The main sticking point added is the fact the save menu is a particularly bad implementation of the stodgy, slow PS4 system save management menus. The real game changer, though, is the expansion of the high speed option. It goes from a useful 2x toggle in the second PS2 release to a 2x or 4x option in this release. Coupled with the gambit system, it really takes a lot of the fat out of the game and feels like something that belonged in there in the first place. It's so easy to toggle on and off it ends up being hard to wander past stuff by accident due to the original game's alert system where it beeps at you when you walk near something.
Anyway, the original game was of much higher quality than I remember. The standard of the facial animation in cutscenes took me by surprise and the voice cast is of a good standard. Kohei Takeda is mediocre as Vaan and Marina Kozawa is dreadful as Penelo (both their only game roles) but the rest of the cast are excellent, particularly Rikiya Koyama as Basch, Akio Otsuka as Judge Gabranth and Mie Sonozaki as Ashe. I know the English translation and dub get a lot of praise, but they do work from a high quality original - not always the case.
Finally, the soundtrack. They actually put three versions in there! First is the original PS2 chip synth track, which is one of my favourite sequenced soundtracks as Hitoshi Sakimoto's arrangement is so well done it could easily pass as streamed until you hit pause and the notes trail off with the reverb as it all stops. Second is the 'soundtrack' - this is the version that Sakimoto made before squeezing the samples down to fit into the PS2's memory. Third is a new recording of the soundtrack which sounds like a mix of modern synths and some live instruments too. A great feature is the way that when you choose your version, it smoothly fades into your choice at the next measure. A small detail, for sure, but one which shows how important the music is.
Overall then, I'm really enjoying this. I'm finding it a lot less aggravating to play than I did originally thanks to features like the autosave on loading boundaries (I've been wiped more than once due to someone getting aggro on a tough enemy without good reason) and areas like the infamous sand sea are rendered much less fiddly when you can blast through on 4x. Even if you didn't enjoy it first time around I'd say it's worth taking a second look. It's aged better than most games of its vintage and a lot of the wrinkles like Mist Knacks/Quickenings having their own charge bars instead of using up all your MP and the ability to invert X and Y camera axes independently mean that it stands up pretty well in its own right.