Strong World was actually written by Oda, he only worked on character designs and approved story ideas for the previous films. That's pretty rare for movies based on shonen series like this. The upcoming One Piece Film Z is also written by Oda so it should be pretty good as well. It's about a former Marine Admiral turned pirate and Aokiji will play a big role. http://onepiece.wikia.com/wiki/One_Piece_Film_Z I like how Z's Jolly Roger has an upside down Marine logo in it.
I read something recently that Oda said he has a notebook that he writes down future storylines in but he had to start tossing some of them out or else the series would never end. Thought that was pretty funny.