A problem with FFXI is that you’re almost forced to have other players to get anywhere in the game. If you’re anti-social, this game is absolutely not for you. You’ll also spend quite a bit of time grinding levels and while it isn’t as repetitive as PSO (Like hitting a 3 button combo over and over again), you will be doing much of the same thing over and over again (Engage mob, pay attention to players TP levels, throw a weapon skill out, skill chain, etc etc).
Don’t expect to get far in the game if you can only play in very short bursts, if you can maintain at least 6 hours a day, you should be fine. But if you can only play for 2-3 hours tops, don’t bother, you will get nowhere at all as parties can take very long just to form up at the higher levels.