The general content is fairly easy. The main storyline, the 4-man instances, the initial primal fights, these can all be completed mostly by yourself.

Then there's the more challenging content. The initial end-game stuff like the hard-mode primals, Crystal/Syrcus Tower, some of the higher level 4-man instances, and Coil 1-4 are all relatively mid-level difficulty. Admittedly, some of the difficulty for this content is finding the requisite number of people needed to do it.

Finally you have the harder content. Extreme primals (These are a challenge. Most people can beat them with little difficulty, but they all have mechanics that make them challenging, even with a massive iLevel delta), Turn 5 and the Second Coil (Turns 6 - 9).

TL;DR : There's enough content in-game and on the way to provide a challenge to 90% of gamers. If you're asking "Is it easy when compared to WoW or other mainstream MMO's", the answer is No.