I'm playing through it now for the first time. Full disclosure I'm playing the english patched IZJS on PC via PCSX2, and I've just finished the whole Panelo and Ashe rescue from the Leviathan bit.
For starters, holy shit I almost didn't even get as far as I did because I got so damned tired of fucking linear underground dungeons and sewers. After the initial tutorial hour in Rabanastre, it's like 5-6 hours of gameplay before you actually get to go anywhere that isn't brown or tan colored and has more than one branching path (thank christ for IZJS's L1 fast forward). Admittedly, once I got out of the passage and beat that giant spider boss (the first proper boss in the game it seems) the game started to grow on me, allowing a bit more freedom and exploration. And the exploration has been surprisingly fun, even in the still mostly restricted area of Rabanastre and its immediate surroundings. Lotta great environment art (though helped by PCSX2 upscaling), and the mob design is certainly a bit more interesting than most other FF's standard beginning enemy fair. Wish the maps weren't so disjointed, but I get that it's probably a limitation of PS2 hardware. The music is serviceable, but no way does it come close to the level of Uematsu at his best.
The battle system has its merits, but at least at the start I really wish there was more to do than just straight melee attack with the occasional healing spell in the beginning. Cooler technicks and attack magics have taken too long to unlock. As OP said, though, it is basically just ATB with field movement, and I don't have much issue with that. I rarely use gambits, but I also like the more precise and tactical micromanagement anyway. I just started using quickenings (though was given no explanation on how to use them), which have this kind of quick-timey mechanic to them which I guess is alright, but it seems completely random whether you'll actually get a button to press for another party member to continue the chain regardless of how quickly you reacted on the previous one. The shuffle also seems to be far too random to be of any real use. I will say this though, it's one of the few final fantasy's that actually presents an ongoing and significant combat challenge in the form of marks. Some of these were tough, admittedly sometimes just kind of spamming a shitload of potions and phoenix downs kinda tough, but it was nice to have something to keep me on my toes while leveling (and actually having to use stuff like attack items and elixirs). Genuinely love the marks system. Also as always I like the fact that I occasionally risk running into some uber powered or higher level mobs in the field, gives the game a bit more depth and genuine risk when out and about. Nothing like feeling you're badass enough to take on a wild Saurian only to nope the fuck out 10 seconds later when balthier goes down on one snap to the noggin.
I'm not crazy about the Zodiac job system and licenses. While the fact that LP is earned via mob kills and is thus infinitely farmable is comforting, it's a little daunting trying to figure out where to go to properly balance your party in the interim. Licenses to use weapons and armor is straight up stupid, but the choice to prioritize between a leg with more attack bonuses versus one with more health bonuses versus one with more remedy/potion/item based bonuses is kinda neat. In practice though I've gotten to the point with nearly all my characters where I maximize health and attack first and then job specific stuff later. It's annoying as hell to find a neat weapon loot (which there are far too few of, another gripe) but be unable to use it because its license is stuck behind a chain of stupid "one more gambit slot" squares. And as I've said, the tangible rewards for exploration usually in the form of loot have been extremely lacking. 99% it's more potions or eye drops or some such, and monsters only ever drop what appears to be glorified vendor trash, even when I get chain mob kills (another unexplained mechanic). Granted I haven't explored the bazaar system that much, but it's yet another one of those unexplained "throw shit at it til you get something" kind of systems requiring a wiki at the ready which I absolutely hate.
Hoo boy the story though. I'm sure there's some great epic hidden in there somewhere, but by god if it hasn't been a giant mess of esoteric name dropping and lore dumping for most of this first act. It's taken me forever to try to memorize the names of all these damn people and places, especially when that intro drops it all at once expecting you to have some kinda notebook at the ready. Other FF's were far more piecemeal and better paced in the unveiling of the world and its characters, whereas thus far FFXII has been a chaotic chain of 5 minutes of fame half characters. Vaan is for sure annoying, but obviously the fish out of water protag trope and tolerable as such. Balthier sounds like a total douche, though, and needs to speak as little as possible. Which brings me to another thing, the voice acting in this thing has been so off kilter. Some scenes are really great, while some are absolutely cringeworthy (that faux Indian accent from that old guy Dalon or whatever is probably some of the worst I've ever heard). Granted jrpg's have always had that kitschy melodrama feel to the writing and voicing, so it's mostly been par for the course. I haven't finished the game so I can't really comment on the story as a whole, but at least there's hope that it gets more interesting. The idea of Basch being some kind of Dark Knight esque anti hero is cool, though the "herp derp btdubs I have an evil twin" reveal was stupid.