Bad One Piece is a reaction of a fan that realized the quality dropped on a manga where we thought it would never drop. Is a reaction to being disapointed when you never expected to be disapointed. So we should be able to understand it instead of jumping at his throat.
I'd point out that most long running manga get worse with time; not only terrible ones like Naruto or Bleach, but also classics like Dragon Ball or Fist of the North Star. But One Piece did seem like a special case where the author never gets tired of his own creation, and in fact, interviews do point to that: what with Oda himself admiting that he has so many ideas, plot points and thing he wants to experiment with that if he were to put them all to use, One Piece would never, ever end. So I take it that Oda enormously enjoys drawing One Piece and that he has ideas to spare, so it's weird the quality would drop after all. . .
. . .now, to me, current One Piece is not "Bad". . .but it is definitely "Worse", comparatively speaking, than the past, better days.
And it's a bit of a shame, cause Dressrosa is overall a good arc. . .but it should be excellent, not good. Right now it's plagued with too much stuff that ranges from mediocre to "is that really you, Oda?". Like the lack of focus, off-paneling everywhere, the crew being more side characters than active characters, and uncomprehensible writing decisions. And again, it's a shame, cause it does have moments that are great, 120% Oda stuff, like blocks B and C, which are so good.
Since the Usopp Cataclysm that made people want to burn Oda at the stake, accelerated pace issues aside the chapters have been good, with this week's being specially awesome and giving us plenty of promise, and it's hard not to get excited over future developments drawing near, like Yonkou arcs and whatnot. But right now, my biggest wish is that Oda blows all his load on Dressrosa's finale and leaves us all completely satisfied. If every chapter from now till the end is at the level of 747, then we're set.