The problem, as I see it, stems from a Trend in gaming that began in the mid-eighties in TSR. For the first time, you began to have series of novels set within the gaming worlds they created. Dragonlance and the Forgotten Realms are prime examples of this. You not only have sourcebooks coming out to describe the world, but you then have major characters and plotlines written within those worlds. This is all fine and dandy—to a point. I mean, I loved the Dragonlance novels, and I would STILL love to run a campaign set during that story (with parallel heroes, rather than the 'main characters' of the novels). But for me, there would come a time where I would have to stop letting the authors dictate the course of the world, otherwise, my players would be doomed to obscurity and impotence as they weave around the major plot lines, but have you real way to affect them. In short, I feel that if you follow the course of a bunch of novels, you are turning your PCs into a 'supporting cast'. For some? That may be what they prefer. I do not.
The Battletech setting is another prime example of Novels dictating the game. When Battletech was first released, it did an AWESOME job of providing an incredibly in depth background to its setting—giving you a snapshot of people, places and happenings at one particular time (in this case, the year 3025, on the brink of what could be the 'final' war to reunify the 'Star League'). This left all KINDS of options for what to do from this point. And then....novels happened. And a sourcebook happened, jumping the setting ahead 25 years and describing, in some detail, that 'final' war and its effects on the setting. And even before all this could settle in, a new series of novels and sourcebooks introducing MORE sweeping changes as the 'Clans' invaded the known galaxy. It was really at this point that I first attempted running a game within the setting. We began shortly before the Clan invasion and played for a bit into it. It was fun. But more novels and more sourcebooks kept coming out. And in them, so MANY details were provided that it would make it next to impossible to run a major battle or campaign, because it would be completely stepped on by the official 'canon' of the setting.
The 'end game' of a campaign for me is what is currently going on in my Vermillion Star Wars setting. With the players operating as major leaders and heroes on a galactic scale—nearly on the same level as the heroes of the movies. This gives their actions a LOT of weight and impact on the world around them. Now, I realize that not all campaigns will go on for 19 years, and that most never even get close to an 'end game', but it is always nice to have that option.
When the Star Wars RPG came out in 1987, it was already 4 years 'after the fact', as far as the movies were concerned. And there were VERY few novels or even comics expanding upon that setting. Thus, when my campaign began in 1991, I had a pretty well established setting, but one where I knew the major events and could work around them—and add to them—without fear of breaking 'canon'. Coincidentally, right about the time my campaign was moving past the movie storyline, the series of Zahn novels (Heir to the Empire) came out, detailing events five years after Return of the Jedi. With some discussion with my players, we decided to jump our own campaign ahead those five years and play within THOSE events. Again, with all three novels out by the time we did that, we could easily weave our own stories in with those presented.
It was after Heir that the REAL slew of novels and comics began. I stuck with it through some of them (Dark Empire, Jedi Academy), but I very quickly found it to be frustrating, constantly scrambling in response to what someone ELSE wrote—and often to things that I felt were down-right stupid and poorly written. How could the players ever be free to really 'do things' if I as a GM was not in control of my own setting. That's when I made the conscious decision to break things off right at that point and forge my OWN story—largely based upon the actions of my players, and on my own views of what the SW universe 'should' be. And honestly? I can't think of another way to run a game. Reading novels/comics is one thing. Gaming is another. The former are GREAT as a source of information, but should never be allowed to overshadow the latter. After all, the point of games like Star Wars is to be a hero, not an 'extra' in someone else's story and universe. So my advice to other GMs is, take what you can from a setting—then make it your own.