FFXII was a truly groundbreaking title, its technical achievements too hard to list because of how numerous they are. To give an idea of why it holds such a reputation among fans, I'll list some of its achievements below. https://twitter.com/luvileen/status/1343611940845748224
The most obvious aspect of FFXII is the character models and environments. The game has some of the best graphics of its generation. The reason behind this technical feat is the focus on the textures of the models, items and environments rather than making them more polygon dense
FFXII's cutscenes are off the charts. Yasumi Matsuno gave specific instructions to the cutscene director, Jun Akiyama, to focus on the quality of the cutscenes instead of the total cutscene runtime.
Moreover, he was instructed to create detailed cutscenes that only the most attentive players could fully appreciate.
One of the most impressive aspects of FFXII is the character facial animations. Takeshi Sadohara worked hard to implement subtle character animations in FFXII's cutscenes. This was especially a huge leap as the previous FF games were incapable of implementing this.
FFXII's sound effects still are a very immersive aspect of the game. This is courtesy of Tomohiro Yajima, the sound designer of the game who took it upon himself to implement the sound effects in the then latest technology. He also did Vagrant Story's fantastic sound design.
It also had highly impressive wind physics. The amount of bones in the character models were also increased. FFXII also had its own lightning engine. An especially impressive example of this effect is this cutscene where you can actually notice the reflection of the water surface
FFXII also revolutionized the way video game localization was done. The process began an year before its launch and was handled completely by two people, Alexander O. Smith @aokajiya and Joseph Reeder @josephreeder. They were given a huge amount of leeway for the localization.
They took it upon themselves to completely handle the process on their own to maintain consistency in the quality of FFXII's dialogue. A detailed interview on the same topic can be found here. https://www.eurogamer.net/articles/2017-07-14-a-translators-tale-inside-the-building-of-final-fantasy-12s-ivalice
The voice acting was also splendid. One of the biggest achievements of the game was translating the stylistic Japanese voice dub into a neo-realist English dub. The actors were given time to understand the characters and implement them.
According to @gideonemery, voice actor of Balthier, the cutscenes were already done before the dub, aiding with visual context. This led to a very natural and well translated English Dub. It's quite possibly the best English dub for any JRPG, ever.
The combat was one of the biggest achievements of the game. Battle Director Hiroyuki Ito crafted the gambit system and the ADB systems as an evolution of his vision to create an ideal combat system. As a result, a battle system was created having real time strategy.
It was a robust tactical system having the engaging aspects of action battle while also giving players great customization and strategy. The animations and combo mechanic gave it immersion, which the gambits and the license board added freedom and tactics to the battles.
By removing the random encounters and significantly reducing the cooldown time for commands, it removed the chore and the variety in bestiary avoided repetition of similar strategies. FFXII's battle system was crafted with the utmost attention to detail
The programming director, Takashi Katano, describing his work as tedious and time consuming. Their work paid off at the end, as they created one of the most refined and robust combat systems in gaming.
It also recieved praise from the directors of Dragon Age Origins and Xenoblade Chronicles, both of them would emulate FFXII's gameplay template and implement it into their own franchises
This, among the 5 billion other things this game did great, is why I think it's a masterpiece
This, among the 5 billion other things this game did great, is why I think it's a masterpiece