Just an idle reflection based on various playdates over the past year. My DS isn't the easiest child on a playdate (he tends to burst into tears at the slightest injury, yet has no qualms about provoking playfights), it's just interesting that when some children come over the games are quite imaginative, require little supervision, and disagreements are shrugged off; with others, the house gets trashed, there are tears and tantrums (from both of them). And it seems quite unpredictable based on the personality of the other child.
My best guess is that it has something to do with parenting style (from what I can tell, the playdates that work are with people whose parents take a similar line on behaviour in terms of when they intervene and when they don't). But maybe it's some sort of complex "balance of power" thing...