Why was FFXI so great?

[Laraul]

I am one of the very few players on this game, that have never properly played Final Fantasy XI. But I see so many people proclaiming how wonderful and great the game was.
So I want to know, so's I can try and compare it to FFXI, what were the best things about FFXI, and what made it so amazing? And also, why did Abyssea (if that's how you spell it) "ruin the game" as some people have said?
Please, i'm very interested to read about how great the game was.
Try not to write essays, if you can :P

In all honesty they are just reminiscing about old times. "Back in the day..." kind of talk. Obviously since FFXI is still going they can continue playing it if they wished.