Most of my campaigns are Sandbox style and the game I'm running right now is a VAST Living Sandbox that has a lot of instances of rippling effects across the campaign.
I'm running a Mekton Zeta game, the games are set up as if the campaign is an Anime series. The main name of the series is Darkest Eve, with the individual seasons having their own names, Rogue Queen Saga for the first season of 24 'episodes' and Cast to the Black as the second season. There are 4 seasons scheduled, totalling 96 episodes, with the possibility of a few more to wrap up the campaign if needed. Of course, the players have the option of canceling the series at the end of a season, but they won't get to find out what happens in the story if that happens. Yes it's blackmail, but if you kill the story before it's done then you probably will never know the end. The series is set in space and has giant robots that the characters get to pilot around, there are other races and space battles along with going out to a great big asteroid field to do some mining. The story for the beginning of the campaign is that an officer of a galactic territory is leading a crew to find what is called Lost Tech. This lost tech is from a civilization that predates all of the civilizations that are around now, even humanity (BTW, Earth was lost a couple of thousand years ago. Well, the entire solar system was lost.). Now here is the part I wanted to get to, the story.
The group hasn't been directly told what the main goal of the campaign is. They know what the story is and are helping it unfold, sometimes in ways I didn't think of. I've given them the option of me directly telling them what the main goal is but they haven't wanted me to reveal that yet. Mind you, the goal doesn't mean they will know the story. This is how I am trying to keep the interest going in the campaign for the 96+ games that I have planned (loosely, I gave up on planning it out fully when the PCs altered things a bit with their actions). I have given clues to what the main point is, but I have created a number of 'Side Quests'. These are making up the main part of the first part of the campaign and they are rather fun and even have an effect on the game world. This is also giving the players reason to explore the game world (or universe in this instance) since they don't really know what the direct goal is. It's been my experience that if the players have a direct goal they will pursue it, often forsaking everything else for it. This way they get to explore and shape things more their own way.
2 main problems with this style of storytelling:
1: Not enough information to keep the characters moving in any direction. PC's can get lost or lose interest if there isn't anything going on.
2: Too much information. PC's can get lost in the information and with all the stuff that there is to do.
I have set up a work around for that, the group has a mission that they are on, searching for Lost Tech. Anything that deals with that they are on top of. Everything else is just icing for them. Whether or not this is the main plot or goal of the series has yet to be seen, heck it might even be a side quest. Am I ever going to tell? Maybe, maybe not. MUAHAHAHAHAHAHAAA!!!