You haven't missed out on much. To sum up the first series at least, they took one game and stretched it out across four full priced disks. From what I recall of the second series they tried to actually implement improvements over the titles but they were minor at best and not really worth the triple price of a normal game. The concept was neat at the time (i.e. when the first part of the first game came out) and a lot of work was put into the setting but A) other games have since done the same concept but better (like so many actual MMOs these days as well as games like FFXII which was offline FFXI), and B) getting into the plot is a fool's errand outside of Japan since that's where the majority of the supplementary material is trapped and unless you're a major fan it's not worth the effort to look up.
And when I speak of supplementary material, I speak of a couple of anime, a number of manga, a movie, as well as a few other games (and the series is rather self referential to the point where the previous game brought in protagonists from all over the series at the time and with just the material that made it out into the US you would be hard pressed to recognize even a third of the cast).
The only real reason why I can think of anyone would want to get into it now is because of the early/mid 00's ascetic of what an MMORPG would look like (or more accurately, the prediction of this decade's MMO ascetic which, unless you count the Phantasy Star series, was pretty far off from the mark).