I like role playing because it's two people creating a story that they both love, bounce ideas off each other, and the thrill of waking up to see how did my partner continue the story? It also challenges me be a better writer because I have to think about what I have to push a story forward that my partner will love or hate, in a good way, and without creating complete unnecessary chaos.
But I personally have always been a primary group roleplayer, it's how I started roleplaying as well.