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.