I haven't seen a lot of One Piece. I think I caught a couple of episodes on TV once, and I know the basics of the show and characters, but I haven't seen anything that really made me want to seek out more. The series has some aspects I like, but they aren't the primary focus and it's too frustrating to see those elements perpetually sidelined for typical shonen fights. However I recently watched the sixth One Piece movie, Baron Omatsuri and the Secret Island since it was directed by Mamoru Hosoda. While the story was nothing to write home about, the direction was great and the animation was fun. At times it was almost like a cross between Hosoda's other films and Masaaki Yuasa.
The character designs have been simplified enough that they can easily be animated, much more fully than most anime (including most of the other One Piece animation that I've seen). Compare this shot of the characters as they appear in this movie...
.... To this picture of their designs elsewhere.
I've seen people refer to that usual One Piece art style as "very simple," presumably compared to other anime, but to me it looks just as bogged down in individual hair strands, muscles and fabric wrinkles as almost all anime and manga these days.
Anyway, in this movie they're handled very loosely, and heavily stylized. The exaggerated perspective is probably one of the main things that reminds me of Masaaki Yuasa.
As with lots of anime over the last decade, it does suffer from some incongruous CGI like the giant fish in the above image... Other than this instance, it's mostly just used for moving backgrounds though.
And of course since it's a Mamoru Hosoda film, it's full of wonderful deep compositions and many scenes with nice muted colours.
The original character designs for the movie are also pretty fun:
I have a feeling the story would have had more weight if I were already invested in the characters from having watched the TV series, but even with my limited knowledge and no emotional attachment to them, it was still a pretty fun 100 minutes.