Some of the successful MMOs over time were successful simply because they've done something different from each other, which is why we ended up with "EQ styled MMOs" and "UO/AO styled MMOs", nowadays it's "WoW styled MMOs" or "Your MMO is dead." Like Rift for example was almost a spitting image of WoW even down to the font settings, it's fun at first, but you learn very quickly you're playing the same game you played in 2004.

People do want something new, yet also not something that acts like it's new to the world of MMOs (i.e XIV's original launch), yet XIV had good concepts to turn it into something different and unique while retaining some of what it's previous FF MMO did, i.e not locked into 1:1 Class/Character.