I hate huge world-changing metaplot.
The Chaos War happens, and Krynn becomes a world without gods (again) and magic (mostly). Krynn has been through so many cataclymic events in such a short amount of time that the entire Crystal Sphere needs a sign on it saying "Welcome to Krynn. The Gods are currently: IN", changing it as needed.
Spellplague and the Forgotten Realms becomes some twisted post-apocalyptic version of itself. (Since I started playing Realms in 2e, the Time of Troubles has always been backstory to me, so I can't count it in my experience, and events like the Dawn Cataclysm and Karsus's Folly always happened in the distant past of the setting, the return of the City of Shade was big, but it was cool as a way to bring the Netherese into the modern era)
In Old World of Darkness, the Reckoning destroyed all the Wraiths, and made it so that Mages essentially couldn't planar travel anymore without it being incredibly dangerous because of a magical barrier formed from the shattered souls of all the Wraiths. I think it was a way to force Mage plots to be more Earth centric instead of walking around alternate realities so much , and get rid of Wraiths in the process, but it seemed very heavy-handed (and surprise, surprise, new rulebooks for the aftermath, and whole new product line for the Hunters that appear after the dust settles).
I like a little metaplot, the idea that adventures come out set a year or two after adventures that happened before and build on what happened, or that sourcebooks reference recent events and create a slowly progressing series of "current events" that don't radically change the world, but instead detail what is happening. It gives the sense of the world being "alive" like a real world and not a static snapshot of a world.
It's only a big problem when it becomes these huge events which completely change the tone of a setting or invalidate huge chunks of materials, which practically speaking seem like just a way to sell more novels and sourcebooks.