They didn't do it first...they just did it best.
I've played plenty of tactics style games since picking up this title (Disgaea, Stella Deus, to name a couple), and I still have yet to find a title that does what FFT does better. They took all aspects of the game, from character development to customization, and they made it simple, elegant, and effective.
So what makes this game so amazing?
Story - an incredibly in-depth story with plot twists and amazing characters. Artwork - it's done in an almost cutesy "precious moments" style, and yet the characters are capable of lifting wine goblets and swirling the liquid inside. I think "deceptively simple" is how I would classify it.
Gameplay - At first glance it appears a bit restrictive, until you learn the strengths of each class and how best to use secondary abilities and how to mix and match them to create crazy powerful characters. Dual-wielding knights? A summoner/calculator? These are just a couple of the more powerful builds available in the game.
All in all, this game is one that must be played by anyone who loves Final Fantasy or Tactics-style gameplay. As I said, they didn't do it first...they just did it best.