Robert Zemeckis on sequels:
Most sequels, you’re behind the eight-ball on them. When audiences clamor for a sequel, what they’re really doing is expressing their enthusiasm for the movie they just saw. And that means they’ll have a love-hate relationship with whatever comes next, because they want it to be the same movie, but different. If it’s too similar, they don’t like it. And if it’s too different, they really don’t like it. There’s nothing more difficult.
I think I've told this story before, but here goes. My feelings about sequels, like my feelings about almost everything creative, can be dropped into one of two buckets: the feelings I have about other peoples' work, and the feelings I have about my own work.
I'm not against anyone else producing sequels to their work, or creating stuff that works serially. Vampire Hunter D will probably continue as long as Hideyuki Kikuchi can hold a pen, and while it may not be great art it's great pulp (and maybe in that sense it is great art-of-a-sort). The seven-year-old in me kinda hopes we get to see Star Wars movies from now until I keel over. (The Fast & Furious movies, too; they're such glorious nonsense, I can't help but like them.)
My point is that other peoples' creative decisions are their own to make, and I'll enjoy them or not, depending on the overall results.
But when it comes to my own creative decisions, that's another story. If I can help it, I'd rather not write a sequel to anything I produce as long as I live, because that seems like a poor way to manage things. To my mind, it's like a failure of my own creative decision-making process — if I ended up creating a sequel to something, it's less because I want my audience to have more fun, and more because I failed to recognize the proper scope of the story I wanted to tell.
See the difference? In one case, I'm just another fan; in the other, I'm the guy in the driver's seat. I feel obliged to hold myself to a different standard in one case than I do in another. A big part of why is because I see in myself a lot of the impulses that Zemeckis talks about in that bolded section above. Fans, myself included, have the impulse to treat the thing they love as something to lie down in and go to sleep in, rather than use as fuel to propel them to new destinations. The same thing over and over again with only the slightest of variations is seductive, but also closed-ended. I'm leery enough of my own impulses to indulge in it that the last thing I want to do is give anyone else an excuse to do that with my own work!
Again, don't take this as a slap at you if you like things delivered that way. I don't have any choice but to operate by different standards as a fan versus as a creator.