Indeed. The good RPer is one whith whom you enjoy to interact.
But the only criteria I would like to point at is being inRP at any cost.
I mean that you will not use OOC even against a newbie who is talking about his characters or something of that sort.
I found out that when you keep playing and such person sees how you do it, he understand what RP is even better than when you are trying to explain that to him in OOC manner.
I'm a fan of trying to find a way to get all the role play done on the forums to be done in game. Problem is, I don't think it is possible with Freelancer.
The quality of RP is highly subjective and depends on your tastes. Personally, I prefer witty humour and/or an interesting and bizarre conversation than the usual, "you killed my parents/you are my enemy/money or die" crap most players I meet produce.
RP is not a weight or colour- you cant judge what is better or brighter RP then others RP. depends on player and his skills/willing to RP.
some people that have impressive RP skills sometimes got sanctionied because lack of RP, or some people that only read few things about faction and came here a week or less can RP better then some who here more then half a year