When it comes to campaign scope, bigger isn’t necessarily better.
It’s an easy trap for a GM to fall into, especially when a game takes off faster or goes on longer than they’d originally expected. In classic Katamari fashion, many GMs just pile on a broader, bigger world when the PCs exhaust or get tired of the old one. It becomes an arms race of size and scale. Saved your village? Excellent! Now go save the world.
Unfortunately, this embiggening is so common that saving the world in any game can feel cheap and rehashed; a cookie-cutter goal offered up by a GM unable to find a more original way to motivate her players. As important as saving the world is, it doesn’t feel important because we’ve all seen it done too much and too often to care anymore.
The reason stems from a combination of distance, assumed victory and a need for personalization. “The world” is much too distant a concept for most people to easily quantify. If you save a town, that’s maybe a few hundred or a few thousand people whose lives you’ve saved. We can almost picture them, all gathered together, cheering and applauding their heroes.
Now try doing that with six billion. In order to see them all at once, you’d have to be so far away that you couldn’t make out a single town, let alone a face. You have only a vague notion of your genuine impact because it’s dispersed over so wide an area. Now you’re not saving people, you’re saving a planet, and planets don’t cheer so good (what with the lack of arms and all).
The second problem is that if the goal you give your players is “save the world,” they know from the start that there are two possible outcomes: either they succeed (and end up roughly where they started, with a non-blowed-up world) or they fail, and they aren’t alive anymore to care (what with being part of said world that was not saved). When “we don’t care” is your loss condition, it makes it very easy for players to disconnect and not be driven in any personal way toward the goal. “Eh” is not a sentiment that urges anyone forward.
All this comes back to a need for personalization. What often makes us care is the individual impact – how our actions affect our own personal monkeysphere. We’re motivated by things which matter to us uniquely. Saving the world matters to everyone equally, making it easy as PCs to say “let someone else do it.” When what’s imperiled is something only you or your group care about, there isn’t anybody else who can step up to the plate. It’s up to you, and only you, to make a difference, and everyone or everything affected by the journey and the victory is connected to you or known to you personally.
And it’s very hard to know the whole world/kingdom/empire personally (unless you let someone play Wilt Chamberlain as a bard, in which case, you have bigger worries).
That means keeping your campaigns (even your big, monumental, galaxy-spanning campaigns) small in at least some respects if you want to keep your players hooked. “Small” here being a relative term meaning “a more manageable part of the whole.” If your campaign is the intergalactic sort, a single planet or solar system could be considered ‘small,’ because it’s still unique amid the hundreds and thousands of systems or planets the players may come across. Similarly, even if your entire game world is a single city, you’ll want to put a little focus into particular neighborhoods (Sigil’s Hive, Brooklyn or 6th Avenue versus all of New York City, etc).
The goal is to distinguish the larger everything-verse of your campaign world from the particular section of it the PCs consider home, and would fight to protect, uplift, or avenge. They don’t have a choice about what game world they’re playing in – you decided that when you pitched the game in the first place. But they do get to decide what portion of it they call their own and make their mark upon, and that’s the part that will matter much more to them than the vague notion of the larger world it’s in.
Respect that choice and that uniqueness by bringing it into the actual plot of your campaign – talk about how whatever great thing it is you want them to do or avert will affect their personal monkeysphere. That it also affects the larger everything-verse is secondary – the little corner shop where their deceased guardian took them every Sunday for ice cream is going to get blown up, and dammit, we can’t let that happen!
When saving the world is an afterthought to saving their little corner of it, you can often get even the typical benchwarmer players sitting up and engaged because they now have skin in the game on a personal level. And that makes even armless little planets want to cheer.