Great writers, bad runs
What are some runs where the top industry writers turned out some mediocre story arcs? Instance where reliably amazing writers just didn't hit the mark they normally have no trouble with? I'll start with two:
Brubaker on Uncanny X-Men. Ed fell into the same trap a lot of great writers do will writing the X-Men. The cast of characters is so large that a lot of writers have trouble focusing in and the stories end up wandering about aimlessly.
Andy Diggle on Shadow Land. It's hard to believe that mess was written by the same guy who wrote Losers and a bunch of Hellblazer.