I don't understand why people think the art style is weird, maybe it's just me, I don't know, but on another note; One Piece is my favorite anime for a number of reasons.
1. The characters are fun, interesting, and have a whole story.
2. You can laugh, cry, smile, be angry while watching this series, even in one episode.
3. I just personally enjoy pirates.
4. The theme music is amazing.