FF8 is the richest experience in the series. Never before had there been a story with so many threads that the player could follow. Deep buried secrets all over the place that added to the experience for those who loved the world enough to explore it thoroughly. Not to mention the many towns ranging from Steam Punk theme with a beautiful orchestrated style music, to very futuristic locations which include Shumi Village which is more like a high tech Environmental Utopia, to Esthar which is a high tech metropolis. Then there are places like the Gardens which is the most advanced school setting ever. The world feels very much alive unlike most others in the series.
Overall it was just an incredible game that took things to a whole different level. I think one thing that should have become a staple was the ability to increase a character's power through multiple paths; and also being able to trade off those skills to others. You gained abilities using AP and junctioned them, refined items acquired through various means to increase stats; you could even turn off all random encounters. It was a great system that should have been advanced upon. It's too bad many players could not understand it and either tried just leveling up normally or drawing obscene amounts of weak spells; rather than advancing their characters using GF skills the way the game intended.
It is also the first Final Fantasy that didn't need a remake (FF7 does).