It's all a matter of perspective for sure. Something I've been working on putting into words is how I calibrate games to the fun that is happening and the fun that could be happening at the table I have. In terms of pre-planning, I often have notes on what players have done, said they plan to do, and how I think they'll react to things. Often tied with important things I want to build up to for later, so that I can keep track of when those things come up - and updating when new things come up in the course of play to change what seems to be important.
But in that process, sometimes what could be called a planned storyline develops, and sometimes events completely change what I'm expecting. And the times that's happened that I can remember have all been awesome. Most fun I've had running games.