I think the most important thing about a RP isnt necessarily 'following' the story/plot to the T, but more that it's a changing story varying from all the different responses of the players... Which is obvious of course but I have had countless RP's where some players completely ignore posts that they don't 'like' or ignore those who don't belong in their RP-clique (like on MF OTL). Oh and of course godmodding is extremely annoying in roleplays (and still used >_>).
I, personally, prefer to focus more on character development rather than just plot. xD But it differs of course.