The main criticism for me its the pacing. I follow One Piece weekly since 2009,and until Dressrosa,arcs used to last around a year. Marineford was from early Summer 2009 to Spring 2010,Fishman Island was from Fall 2010 to Fall 2011,Punk Hazard was from Early 2012 to Early 2013. And it was good because 1 year is the right duration to enjoy an arc without getting too tired of it. Since Dressrosa,arcs became longer and now lasts years and years,and this gives too much stalling in a series that should feel of 'adventure' and should always shows us new places and new situations. But when an arc is too long,you lose this sense of always be on the adventure.