If I may,
I'm not very familiar with One Piece anime filler beyond the basic gists of some of it (I know several filler arcs existed to promote movies, for example). Yet I've often seen G-8 hailed as the best, if not the only good, filler arc in the series. How is that so?
It's a lot of little things done right, the G8 commander being more than just evil guy on an island. The chess comparison is made to be a big part of the chase, with characters having their traits be used correctly, like Chopper doctoring and Sanji cooking, and Usopp lying. You have the believable plot point of the Merry landing in a big naval base after falling from Skypiea, which makes sense for the Navy to have in places around the world.
I think the big thing the story excels at is, if you didn't read the manga ahead of times, this feels like how the Straw Hats lose all their Skypiea treasures. They just had a big haul of booty, and like other cartoons or anima you're expected to have the Straw Hats remain the scrappy broke pirates because it's the status quo. They abandon the gold for the Merry, or for a crewmate, but no. Plus the characters feel like themselves and not like filler. A lot of the filler is obvious because it becomes surrounded around one character an episode, like all those fillers after Enies Lobby, but here because it's usually two characters or more in an episode, plus with the commander Jonathan, it feels real. Things like Condoriano or Chopper trying to be threatening because Zoro wants him to be and then Luffy being too stupid to realize it's an act, feel real and true to the characters.
One thing that probably doesn't get mentioned a lot is that these were the last episodes animated in that original One Piece style that was retro even by late 90's animation standards because they went high definition/digital with Water 7 onwards, so everything feels like a final hurrah of the old style or studio, They were never given a lot to work with, but it just felt more expressive and fun with G8.
