Well the problem is the early stuff, while the design for Luffy and Zoro has not changed much over the years, everything else has evolved quite a bit. For the time the design for One Piece was unique, most other manga's were similar to the way Naruto was done, which is typical Shounen design. So you had to get past a preconception of how the drawings should look and actually read the manga for it's story. Plus when you look at the early designs of Luffy, and Nami specially, they were kinda basic, Luffy's been the shorts, the hat, and the waistcoat, and Nami was skirt with simple striped top.
It gave off the impression that the manga was aimed at younger kids, so specially in the west it got overlooked due to assumptions on the quality and demographic it was aimed at, the 4-Kids version did not help matters much either, as they took the anime, kiddified it and destroyed any possability of the anime succeeding in the West. Remember this was a time when the internet was still early, so TV dubs were how most of us were introduced to animes. And One Piece made the worst possible first impression, an impression that stuck to with many fans.
You look through the chapters from One piece and you see massive improvements in the artwork, The same can't be said for Naruto, if anything it could be argued the charactor designs in Naruto just got plain lazy, you just have to compare the original generation as kids with the new generation, even the adult versions of the original generation are plain lazy.
One Piece is not an easy sell in the west, I couldn't convince my nephews to read it, even me it took my friend ages to convince me, and if I hadn't watched Naruto and Bleach first I probably wouldn't have given it a chance either. The thing about Bleach and Naruto is they get you hooked from the first chapter, where with One Piece you have to get to the Arlong Park ark to really get to the interesting arcs.
Ah, I see. Yes, that is true. One Piece truly didn't get interesting until Sanji joined the crew, and the first serious arc did not start until the Arlong Arc. I've started reading One Piece from Ch.1 last year, so the drawing style is still fresh in my mind. Strangely enough, it didn't bug me... Though the artstyle has evolved over the years, I already liked it. Yes, it looked childish, but it was consistent and clean (in my eyes). Did I mention the humor that was already topnotch from the start?
As I've mentioned before in previous, I've started watching One Piece more than ten years ago, so I'm totally used to the style already and ventured into the manga already knowing what to expect. It was the German dub, and the voice actors completely nailed the characters and were kind enough to dub the Jap openings (while the US opening version...).
With all that being said, I'm not completely a fan of the female body proportions in One Piece (yes, I'm picky), but that is not a major issue in my eyes. In comparison, Naruto seems to completely scrapped the idea of realistic body proportions for either gender and has sloppy artwork (like seriously, if it weren't for the hair and facial features, some of the women look like men). The artwork sucked back then and isn't that much better now.
I always despised the artwork in Naruto, but I'm not someone who will drop or not start reading a manga b/c the artwork is bad (aka Magi)- but that's just me who doesn't appreciate manga artwork enough.
