FFXI caters to many different playing types as well.
You can solo, party, work on your crafts, item hunt, collect Gil to build up your characters spells, weapons, armor, etc...
I personally find the solo life to be quite pleasing at the moment.
I've raised my little Tarutaru White Mage all the way up to level 10 so far without much hassle, and it's been a blast.
(most people do look at me weird when I say I'm going solo as a WHM though...)
Hell...I haven't even done a Mission yet. I've teamed up with a few parties, but never really got too far with them.
I'm sure eventually I'll feel the need to do so, but at the moment I love just running around, collecting Gil, doing Quests and finding items to use for my Crafts.