There's really two ways to run a role playing campaign. Plot based and character based. In all truth, they can't exist alone. Either one depends on each other, but like a Peanut Butter and Jelly sandwich, its all about the ratios. Too much of one and not enough of the other creates a bad game. The mixture is right, but sometimes it leans one way or another.
Personally, I love a good plot, but when it comes down to it, its all about the characters and their choices. That's why I really like sandbox games, to steal a phrase from our illegitimate bastard child hobby video games. I love just setting things up and then letting the PCs just find their own pace and explore.
However, in the past, I've run all sorts of games. In one old game I ran during college, I basically railroaded my PCs through several massive plots that had to do with the world in balance. Everyone had fun, but it was really forced. Overly so. There weren't very many choices, and I often manipulated them to go where I needed them to go to further the plot. At the time I justified it to myself because I didn't have anything created except for what I wanted them to do. I wasn't confident enough to let them do what they wanted. I both regret it, and remember it fondly. The important thing is that we had fun.
Later in college though, burned out on D&D we played Vampire; The Masquerade. However, I made the exact opposite side of the cord. The characters did it all, with a few exceptions when things got too stale. There were things that happened, but it was because they were what the characters wanted. Or rather after each session, I asked what the PCs wanted to do, and then tailored each session for them. It was too easy. Just a handful of constant NPCs. We actually ran three separate interconnected campaigns, so each of the three GM's were players in the other campaigns. So it was really really easy. We would swap out PCs and events and such.
Right now, our campaigns are great.
The Plague World campaign has been stalled for a bit, but it started out plot driven, but has quickly become character driven. Its interesting to see how the characters interact. Especially when they plot and plan. I love running a highly tactical game, given my wargame roots. It's awesome to watch them plot and plan, only to see the glaring errors while their doing it.
The Monsters, ah, the Monsters. It's not really plot driven or character driven. It's an odd duck. It fails on both fronts, but it is a pure fun. Possibly because it avoids both of them, it succeeds on both of them.
The Ogres. Well, it is far more plot driven then character, because the characters are cut and paste. It is fun, though, because they started out as such stereotypes, they grown as the plot has gone on. I love seeing how such a simple concept can be taken by some good players and run with.
Darksun. Well, it should be more character driven, but we'll see. It could go either way. I started watching wrasslin again because of it. So it could evolve through it, it will depend entirely on the PCs.