How many designers have been asked to make a “GTA killer”, or a “Guitar Hero killer”, or a “WoW killer”? I personally have heard numerous designers and producers working on unreleased MMO projects describe their game in these terms: “It’s like WoW, but…” I just shake my head when I hear this, because the team that is best poised to deliver a successful game that is an evolution of WoW is… well, the WoW team. They’ve got their thing, and they’re good at it. Let’s all carve out our own thing, and be the best at it. Truly great games are made by passionate teams who are on fire with the notion of changing the industry. If you are aiming at a competitor rather than aiming to make something fresh and innovative, you’ve lost.

How to Create a Successful MMO by Jeff Strain.