Okay, so, I thought it'd be a good idea to have a thread detailing the artistic changes that have transgressed since the start of One Piece, both for encyclopedic purposes and for the fun of it. This is an aspect of the series that I haven't paid particular heed to myself so I'm just going to start things off with a fairly simple part of this, which is the animation changes over the course of the One Piece anime. But let's not limit it to that, if anyone wants to comment on the changes mentioned, pick a favorite out of them, or anything else, you're more than welcome to. And if you want to add a step I've missed, which I will 100% will have, send me a PM so that I can add it to this original post when I can ( with a relevant picture if it's necessary please, cause we're trying to get in line with the new Japanese copyright laws as a forum from what I saw, so I shouldn't download all the pictures myself ). If you don't know how to send a PM, you can post it here yourselves ( you thought I was going to say "send me a PM and I'll show you, didn't you? Psyyyche!! ). Jokes aside, feel free to do whatever works best for you, and don't limit yourselves to the animation changes. Art changes in the manga / changes in the character's clothing / Seiyuu changes / writing style changes ( if you feel confident enough to read Oda ). Any artistic change you can think of, don't hesitate to shoot it here.
1) First we have the old style of more traditional and old school anime that basically looks like a depiction of the manga art but with color. Round characters, not many edges to speak of
2) The point where I saw a noticable and noteworthy change since then is when the animation switched to digital, around the Skypeia arc all the way to the Water 7 arc. The characters got mor edges, got significantly slimmer over the course of the change and the noses seems very thin and flat in some cases.
3) Lastly the next changes I noticed were during the Marinefold War arc all the way to even after the time skip and tbh, possibly until now ( Wano excluded since I haven't watched / read that yet). It's when the animator, I'm guessing, found a good balance between the original round character designs and they new skinny ones to make decent one with proper-ish body proportions and higher quality special effects, making the characters look more realistically bloodied, wet, beat, tired, etc in certain situations.
I just caught up to the Wano arc in the anime version, and the biggest animation change I noticed was the change of how haki based attacks are depicted. With Haoshoku haki being depicted as "light waves" instead of the former invisible shockwave style, bushoku being depicted as a dark purple / black and red in its advanced form and kenbunshoku usually being implied to have been used after a character's eyes shine slightly red. Other than that, the animation has settled at a good point with vibrant colors and a nice body structure balance.