I've not played WoW but have a great number of friends who do or did. Most of them if they had previously been FFXI fans said they LOVED WoW... then about 3 months later they had 1 or 2 jobs at 60 and came back to FFXI saying that WoW was too easy.

Apparently WoW definately caters to the casual player like lionx said. It's more user-friendly in that way. FFXI is a hard game to just start up and get going especially without friends. But it seems like there is more long lasting content in FFXI to make it worth coming back to repeatedly.