FFX is the most beautiful RPG i've ever played. It's not the best Final Fantasy, but who cares? It's still amazing!!
As the first FF with the advent of the spoken word and 3-D non rendered backgrounds, it pulled them both off w/o a hitch. This was an incredible feat in itself.
Of course the combat system was a mix of 'tried and true' styles and some new wait-turn styles. It works very well in the context of the game. The world design was nothing less than stellar (big surprise), game engine and mechanics were innovative, and the new sphere grid was quirky, but surprisingly useful.
Also new was the ability to exceed 9999 pts of damage in an attack. at first this makes you feel ridiculously powerful, but just a few encounters with optional enemies in the monster arena, will knock you back down a peg, rather quickly.
bottom line: if you don't own FFX, it's unlikely you're a fan of RPG's. Those of you who do, know exactly what i mean.