Avid Final Fantasy fans better be prepared for change, sometimes change is good :D x
Obviously this game is a LOT different to any other Final Fantasy, the difference being it's online and multiplayer with no particular strict storyline to follow.
It's relatively easy to learn about things in the game, NPCs are a great help and guaranteed in your town or area there are a lot of people willing to help you if you're stuck. The higher level characters and mentors are also brilliant and more often then not if you find a nice enough one they'll help you with a quest.
Fighting solo can be a bit boring, unless you're going for a real challenge. I find partying and meeting new people the greatest hype of the game. Everyone is really friendly and its great getting to know people in different countries.
I put the learning curve at more than 4 hours as I'm still finding out new things as I'm going along.
All in all I think this game is brilliant, it's a welcome change from the other Final Fantasy's, it was defintely worth trying something new with the franchise.
I HIGHLY recommend this game to all people who enjoy online games and even possibly to those who would like a slower paced game than World of Warcraft.