FFXI is not for the casual player. There are casual players, but they will miss most of the meat of the game and all that's left really is grinding XP in parties with people. Just be aware that you'll need to be able to regularly set aside 2-3 hours to really play. Nothing pisses off a group more than you having to leave suddenly and reputation can go a long way as far as party invites are concerned.

The community is overall superior to other MMOs, but the game is almost like a job. It takes quite a bit of work and effort.