Well I think a lot of the appeal of FFXII, for me at least, was from the art direction. I used to run a FFXII site way back when (back in 2003, when we thought the game was coming out in December 2004) so I became very closely acquainted with all of the art and even lots of concept work that was only shown in the Ultimania Omega (I have that too). I've always liked Ivalice the most of all the Final Fantasy universes and, of course, was always partial to the storytelling and themes prevalent in games designed by Yasumi Matsuno, who also directed Tactics Ogre, FF-Tactics, and Vagrant Story.
Honestly I feel like FFXII was destined to be a top-5 all-time JRPG but was ***** by corporate SE early during production. And Matsuno, sick of fighting with the higher-ups for control over his baby, just left the project to rot.
You can still see some of his touch, though—namely in the opening sequence and how it sets the tone with Ashe's tragic character, and in a certain cutscene where Gabranth is ordered to execute Judge Drace. The latter, especially, is really really well written and directed. Combined with the animation, which I still think puts most PS3 characters to shame, the game had the potential to pack some huge dramatic punches
I'd say the beginning of the game until around the Tomb of Raithwall is pretty close to how the entire game should have been. The pacing is absolutely perfect, there's tons of freedom and areas to explore—just remember how closed FFX's areas were—and there's plenty of character development, all shown in cutscenes that show off the game's intricate animation quality. After Raithwall, however, the game starts falling apart, and I just know this correlates with Matsuno leaving production, I just know it
I'll even go out on a limb and say that the first 10-12 hours of FFXII are the best 10-12 hours in any Final Fantasy game before or since. The only problem is that XII makes a lot of promises that it eventually cannot keep
I think a lot of people don't become attached to FFXII because the game is actually quite subtle compared to the more grand JRPGs of the time, so it's very easy to miss a lot of the details that really enrich the experience. For one, the game has a tendency to hide some of its most interesting world-building tidbits in the back pages of its Clan Primer—but man I still haven't come across another game that has put as much interesting backstory into its cities and regions like FFXII has.
The intricacies of the plotline—especially the motivations behind some of the major story forces like Vayne and Marquis Ondore—are, too, usually glossed over by most players. Part of this is due to the dialog, which is beautifully executed but relies heavily on subtext that is not always apparent. Many situations in the story are not clearly explained (just like all good political dramas), and so the full impact of a lot of scenes are often lost.
I played through the first half of the game again this last summer, which is my 6th or 7th time through, and there were still moments in the story where I was like "so that is why he did that" and man parts of the story are so damn good, but most people don't give the game a chance
But otherwise, yes I agree with you, SE dropped the ball with FFXII. It's just the FFXII I see is much different than the FFXII most other people see and it's sort of unfortunate