I'd absolutely point to Space Station 13. A old game built on a terrible engine, but with an active development community because the source is open. Each server runs a slightly different variant of the game, and a fair number of servers enforce "heavy role play."

I'd recommend a server like Baystation 12 if you're looking to get involved in an RP server. A small bit of googling can point you in the right direction.

A long time ago I played http://www.sindome.org but my English was not very good back then. Out of character talking was allowed but with a particular marking (I think it was double parentheses). I guess you can filter OOC talk.

Wow, that's a blast from the past. Seriously, thanks so much for posting that link - I've been dying to get into some hardcore roleplaying and it's nice to know that Sindome is alive and well.