Mercule said:
I finally realized that I'm getting burned out because I've already told the story to myself and I'm just dragging the players along (occasionally, kicking and screaming) with me.
This is a trap I've fallen into as well. I've had campaigns where I became completely bored because I knew what was going to happen in the next four adventures, which might be months of play, and I was basically just trading water waiting for the players to get through the stuff.
Part of the reason for this is that I've gamed with the same people so long, I can generally predict how they're going to react to something. Even when they're heading off "into left field", I could usually know ahead of time they'd do something like that. (Not always what they'd come up with, but knowing that they'd do something unconventional in reaction to a situation.)
In a way, laying out too much of the campaign is like buying a TV show on DVD where you saw the first half of the season, but not the rest. However, before you can get to the new episodes, you have to watch your way through all the early ones you've already seen.
It's boring.
To change this, I've adopted two tactics. The first is that I simply don't plan ahead. I try to come up with the next session and that is it. (I tend to be an off-the-cuff DM anyway, so this is mostly about making myself not plan out the sessions.) I get some notions of bigger plots I want to introduce and just find places to drop in the elements as I come up with new ideas.
[As an example of this, in my most recent session, I had the players hired to go hunt down some creatures that were living in an abandoned manor and eating local farm animals. We hadn't done a land adventure in a while and I'd seen a picture of a monster I liked, so I used it. I also dropped a plot element into things, though the characters don't know this yet because they've only got one data point on that graph. I didn't design the adventure as anything more than, "Hey, this would be a find change." I just used the idea I came up with as a holding point for a plot element.]
The other tactic is that I've shuffled out some of my play group and brought in some new people. I also brought back a player I've gamed with for years but whose play style has really changed as he's matured a lot lately. (Settling down does that to some people.) This has resulted in a play group that I can no longer predict. It keeps things more interesting for me because while I have some idea of their typical battle tactics, they are taking some very unexpected tacts when dealing with NPCs, with mysteries, and with the world around them.
One other thing that I believe is normal, though, is sometimes wanting to try a new idea in the middle of an existing idea. Good DMs are creative people, generally speaking. Creative people don't always keep their ideas in a specific track. In the middle of a D&D game, I can suddenly have ideas of a super hero game I'm unlikely to have time to run for at least a year. I make notes, write up some material, and basically let it out of my head, but I recognize that it's just extra creativity and not a reason to end my current game. (Which I already put a lot of time and creativity into.)