I've been re-reading One Piece, and I just finished Drum Island. This re-read has cemented Nami and Chopper's backstories as being two of the best in the series in my book.
It's been a long time since I've read some of these arcs (probably close to ten years now), and I'm glad that I decided to revisit them. Even with poor quality scanlations, the early parts of this series hold up extremely well. Plus, when I get to the longer arcs later on, they should flow much smoother when I can read them all at once as opposed to having to wait a week or two between each chapter.
I've got a long time to go until I've completely re-read the series (I'm on chapter 155 out of 979 chapters), but I don't know if I'll re-read any other long series. Maybe I'll try JoJo's Bizarre Adventure part 6-8, Rurouni Kenshin, or Hunter x Hunter.