Storyline Prior to Game

[Nephera]

Brief summary:

Eorzea was gearing up for war between the city states, then the garleans showed up and plowed down a city, then all the other eorzeans city states decided to band together to fight the garleans and then they....never showed up.. (Maybe they ran into "HOLY CRAP THAT IS A LOT OF DRAGONS"). Because the city states had gathered so many soldiers and it was apparent that they were no longer going to be going to war they started up the adventurer's guilds to keep the economy from tanking.

nifty job of explaining why we have so many adventurers.

[Jennestia]

Brief summary:

Eorzea was gearing up for war between the city states, then the garleans showed up and plowed down a city, then all the other eorzeans city states decided to band together to fight the garleans and then they....never showed up.. (Maybe they ran into "HOLY CRAP THAT IS A LOT OF DRAGONS"). Because the city states had gathered so many soldiers and it was apparent that they were no longer going to be going to war they started up the adventurer's guilds to keep the economy from tanking.

nifty job of explaining why we have so many adventurers.

Yep, and it already beats out XI's explanation of us just..showing up lol. The storyline is great, people that say it's bad likely button mashed through the text parts nor read journal entries -- It's vanilla, you usually wait till the expansions to really get into the meat of the overall storyline, XI is a perfect example unless they sidestep from the story progression as well:

Vanilla = Basically introducing you to the game and certain characters
Zilart = Explains pretty much everything about the past and trying to open the gates of paradise
Chains of Promathia = Fills in plot holes as well as even more truths about the Zilartian era
Treasures of Aht Urghan = Story of an entirely different continent all together (near/far east), as well as goes deeper into Bastok's involvement with a certain situation.
Wings of the Goddess = All about the Crystal War and Dynamis. It also throws in a very detailed story about Atomos and how the vanadiel we know may not even be the actual Vanadiel.
A Crystalline Prophacy = Closing a 6 year plot hole (Sister from the opening of the game.)
A Moogle Kupo d`etat = A fun little story about a moogle mob boss..basically.
A Shanttoto Ascension = All about Shanttoto.
Abyssea = A time/space tear allows us to enter yet another visage of Vanadiel that existed without the Zilarts and Al`Taieu is still in the normal plain whereas our Timeline it's in another dimension. It also explains how the mother crystals are all shattered and you even see as such in Empyreal Paradox (Abyssea) where the Twilight God, Promathia, has mutated into the Dragon God, Shinryu.

So as you can see..Vanilla storylines no matter how you slice it won't ever be as good as the future storylines -- This is true in pretty much all MMOs because the expansion storyline tend to have to detail new features/event systems as well, e.g Campaign is merely the key battles of the Crystal War with the invading beastmen.