Tattersail... that name sounds vaguely familiar, it's been many years since you played hasn't it? Well regardless, welcome back!
The game has changed quite a bit. The lower-level (75 and below) events have mostly been fixed up so you can do them solo, even Dynamis. A lot of new content has been added that focuses more on reward for every player rather than making players help each other out, which has sort of turned out to be both good and bad. It's easier to set up shout groups or just do things with one or two friends and still accomplish things, but linkshells are more social and players in general are more self-serving as a result. The days of going to Jeuno, shouting for help on something, and actually getting help fairly quickly, are long gone.
That being said, there's lots of fun still to be had! Abyssea is a huge new addition that you've likely entirely missed, and there's just a ridiculous amount of stuff to do in Abyssea. It generally only requires 2 or 3 players to do most things in Abyssea, too. In fact much of it can be done solo. If you're returning, Abyssea is where I would start. Start out just by getting a feel for it and set some small goals. I suggest trying to obtain an Azure Abyssite of Celerity as an early goal, it requires going to Abyssea - Konschtat and killing tonberries. It's usually the first thing I take people to do in Abyssea, just to get their feet wet.