Celestial Hills is where you'll want to roll if you're partial to player-generated stories, but be aware that En Masse is taking a laissez-faire stance to its RP ruleset. The company says it will implement naming conventions to discourage leetspeak and real-world references, but it also says that the subjective nature of such a policy makes it difficult to enforce.
En Masse also says it won't monitor out-of-character chat, but it will boot those who "continually harass others." Finally, the FAQ addresses player requests for RP tools like the ability to walk and create custom emotes. "We are working on a list of game features to enhance your roleplay experience," En Masse explains. "[As with] all game feedback, we are evaluating and prioritizing getting it in the game."
[Thanks to Dengar for the tip!]