Your puny poll cannot contain MY answer!
I like metaplots when they describe what is going on as the backdrop to the adventurers' actions - I don't like metaplots when they become "the story."
For example, for my
Traveller campaign, the metaplot is an invasion of K'kree space by something from beyond the trailing borders of the Two Thousand Worlds - the K'kree respond by fleeing toward Imperial space. (I'm calling this "The Stampede" in my campaign notes.)
While this sudden incursion of K'kree into the Imperium is a potential source of dozens of adventure hooks, there is no "adventure path" by which the player characters encounter the K'kree, journey to the Two Thousand Worlds, encounter the alien invaders, and turn the tide, saving Charted Space. The adventurers may follow hooks that lead them into the Two Thousand Worlds, or the Hiver Federation, or one of the client states along the trailing margin of the Third Imperium - they may encounter the aliens, and could possibly learn important secrets about the enigmatic invaders. On the other hand, they may choose to ignore the whole thing and pursue completely different goals, bumping up against this massive migration in the course of their travels only to the extent that the effects of the Stampede are felt across the Imperial frontier region.
This is my approach to metaplots: a sequence of events that affect the
setting directly but the
characters indirectly, events in which the characters may or may not choose to involve themselves and which may or may not be afffected significantly by the adventurers' involvement or lack thereof.