Thriller Bark is an arc that could and honestly should be top 5 (the fucking RPG cross attacks vs. Oars+Moria bits alone should do it but this is also an arc with Usopp v. Perona, Brook's flashback and THAT ENDING) but Hogback and Absalom make it so hard to go through early on. Skypiea absolutely should be higher regarded however. One of the best backstories in the series to date + world building (Skypiea is the longest con in the series, facts) + the genuine feelings of adventure involved + having a genuinely busted antagonist that early on but dealing with him in the ways that each Straw Hat and intertwined person did made for such a great time.
I don't care what some fans say, Armament Haki has been around a lot in the early parts of the manga/anime and the audience just couldn't see it, or it was so weak that it didn't make the heavy black color.
The moment they expanded on the system with Rayleigh before time skip was the moment I was looking extra wide eyed at things like Zoro vs. Mr. 1, the Six Kings Gun/Rokougan move Lucci used to almost end the match with Luffy, and Crocodile getting extra shook before the Water Luffy revelation (and even the climax with Storm casually parting through La Spada). Even little things like Blackbeard talking with Luffy and explicitly referencing Luffy's haki (back when translations used to call it his ambition/spirit no less lol) on Jaya should really have been bigger moments for folks. Observation was always super obvious and straightforward with pre-timeskip applications in Mantra and the Boa sisters.
Seeing Oda outright come and mostly say that the Zoro v. Mr. 1 stuff was not a bad thing to pay attention to all this time later in Wano definitely makes me super excited to see if more of the stuff mentioned above was also related.
The one bit of head canon I have that has yet to be shown as true or not was that maybe everyone at Marineford had been using Armament Haki/Hardening but Oda was pulling the HxH nen thing where inexperienced users couldn't see it/it looked invisible (and we as the audience going along with Luffy & the crew's p