It doesn't matter what the plot is (as long as it's one I like) but I like a literate role play. Not a "script" role play.
Bob: Hi!
Joe: Hi!
Bob: What's up!
Joe: Not much, you?
That's a script. If it was literate, it would go like this: Bob saw Joe and walked up to him. He said, "Hi Joe! What's up!" Joe turned around and saw Bob. "Hi Bob! Not much, you?"
Or you know, something along those lines. And I also like at least 2 or 3 sentences per post rather than 1.