City of Heroes had some player based content, which also fell flat on it's face. That was in part due to engine limitations but also the difficultly in making interesting content instead of just a lot of new content.
Eve would be a data point supporting this. I had some adrenaline rushes playing Eve, but I also could use it as a sleep aid, depending on precisely what I was doing.
I think that one of the problems is a poor conception of what it means for players to create content. The most compelling content for me in Eve was simply the most exciting stuff that happened during nullsec alliance PvP.
In the end it's different largely because they are not trying to be a 'successful' company, instead of kind of a profitable hobby.
This also fits with my current goals.
Instead of paying player characters to grind, and therefore have players consume game content, why aren't we paying players to create game content?