Kinda late to this thread, but OP is pretty decent for the first 300 episodes, of which I recommend you watch One Pace or read the Manga instead due to Funimation's absolute shit tier pacing and literal stall frame timing. Seriously you will waste a solid 1/3rd of the time on filler frames and static scenes because they want to make more episodes.
The writing itself is actually pretty smooth, and the filler content (not animation) actually fits so well you probably won't even notice its filler, because it really adds to the world building and story (and afaik is actually written by the manga author).
Everything after than, just disregard it as a Shonen franchising product designed to make money, like Pokemon.