I just think there are so many mmos (most of them) where you have to roll a new char to play a different job, and most mmos with no choice or "build your own class" outside of rigid boundaries... So the idea of one, just one where there is an ability to play in different ways is really appealing to me. I'm weird though. I liked the player level plus class level thing that xiv used to have too... Again I think it was implemented in a crummy way, but I remember being so excited when I heard about it. Finally! A mechanic that rewarded me for being one of those people who likes to level a bunch of jobs at once! I loved that I would be getting stronger in all of my classes by leveling any of them.
The skills were a nice bonus too. I would have been ok with some more limitations (not being able to equip an ability till the level it was earned in the base class, for example or even something like the "spell points" limitation seen in blue Mage in XI.
I just look at the current battle system and think, can ere even BE a blue Mage? A blue Mage with just 15 spells and abilities? Really? I can't even fathom it. It would take all the fun out of the job.
I feel sad that SE let the armory system flop. It had a lot of potential, and their previous single player games had lots of concepts at could have aided them in making it work (9 people mentioned above... Tactics is another example)