Plotting out the whole story in advance is possible, but greatly ignoring the great potential of the roleplaying game medium. Retelling a novel or movie in an rpg campaign is only scratching at the very surface of what an RPG can do, while barely making use of any of all the many great options that only RPGs can provide, that are not possible in any other medium. And the key is interaction. Or if you want "true interactivity".
This is very true. While I think there is a great deal a DM can learn from more general storytelling techniques, I'm also very wary of DMs who talk in terms of 'plots', since the danger is indeed that
the DM is telling a story, rather than
the group telling that story.
They key to doing this is to plan what factions there are in the campaign, what they want to do, how they plan to do it, and what resources they have.
My current campaign looks a bit like this:
- Big Bad reads old book about artifact. (Before the game starts)
- Someone discovers the artifact and turns into a monster. (PCs might find the artifact, but it could also remain in its secret chamber.)
- Big Bad learns about the monster and goes to the dungeon to look around. (And either find the artifact, or pick up the trail of the PCs.)
- Big Bad will go to an old library. (If the PCs ever go there, he may or may not have already been there and took the book with the info on the artifact with him.)
This is all good stuff.
Another thing that I've found helpful with RPG 'plot' design is the Narrow-Wide-Narrow structure:
At the outset of the campaign the party is created according to some fixed premise - "you're kids off the farm about to head on your first adventure", or "you're agents of the Empire hunting down rogue Jedi", or "you're all pirates" or whatever. And, because there's a known starting point, because the players have fairly limited information about what's out there, and because the characters have limited influence to change things anyway, the 'plot' is necessarily quite Narrow - although the players have choices, the range of things they can choose (or, at least, the range of things they're
likely to choose) is fairly small.
As the campaign progresses, those initial conditions naturally fade - they're no longer at the known starting point, they have much more information, and the characters have acquired power/contacts/money/fame that allows them much more significant influence. Therefore, it's a good idea for the DM to prepare a 'plot' that is necessarily Wide - provide lots of factions, lots of plot threads, lots of mysteries, and let the players tackle them as they see fit. (Generally, I find it useful here to sketch out a bunch of stuff in advance, and only fill in the details about two steps ahead of the party's progress - I can usually predict player actions reasonably well that far out.)
Ultimately, though, those Big Bads are going to need to be dealt with, one way or another. Sure, the PCs don't
have to stop the Evil Cult from destroying the world... but it's a fair bet that they're going to try to. And so, as the campaign comes to a close it's not unreasonable to start building towards a fairly fixed climax - the 'plot' once again becomes much more Narrow. There may well be diversions along the way, not to mention all the stuff that the players should be introducing themselves, but there are probably at least some fixed points you can prepare for quite a long way in advance.
(Of course, this assumes the campaign has any sort of ending in mind. It is, of course, entirely valid that the campaign might be entirely open-ended, in which case Narrow-Wide-Wide is probably the better structure.)