One thing I remember fondly while playing offline Final Fantasy games and other RPGs, was the fun and challenging puzzles you had to overcome in order to complete a dungeon or quest.
So far in playing ffxiv (level 45) I don't recall coming across any thing that would really fill the term Puzzle solving challenges within the game, sure there are things in some Dungeons where you must find and collect certain items to unlock new passageways.
I'm not sure how effective such challenges would be in an MMO or how easy they would be to implement efficiently.
But I feel that if they added this whole new mechanic of puzzle solving quests and dungeons it would break up a lot of the monotony of grinding and repeating Fates, filling hunting logs all the general kill, gather and repeat type quests.
(Sorry if my sentence structure was so bad and hard to understand, I am suffering a terrible migrain which is effecting the cognotive functions of my brain machine)