1) Massively reduced amount of fake out deaths and sacrifice scenes that get nullified only a few chapters later after milking the readers' emotions earlier on. Really drags down the overall quality of the story. Either cut the crap and leave out those bs scenes or actually man up and deal with actual consequences and let the characters stay dead.
2) Much more variety in terms of arc structures. Literally every single major arc in OP (except for two arcs, which I will touch upon in a moment) follows the same uncomplex formula:
- strawhat crew arrives at a new island
- SHs split up and discover that some sort of conflict is going on, meeting some friendly people (most of the time a young, beautiful princess) in that process
- at first it appears the conflict was caused by the natural development inside the island, but some obviously bad guys appear and have a first conflict with the SHs which usually ends bad for our heroes
- now the conflict is revealed to be set up by the main bad guy(s) through some sort of deception / misunderstanding (flashback time)
- Bonus points if there is a scene where this whole misunderstanding is being cleared up and all the island inhabitants go ”oh nooo that guy we thought did something bad actually had a good reason for that, we are such idiots nooooo”
- Luffy (and the SHs) beats up the main bad guy(s) in the second round which solves all issues and everyone is happy, since the whole conflict was just a misunderstanding/set up anyway
- banquet and leaving for the next island
It's getting to the point where any halfway grown-up reader just rolls their eyes and wants to ask Oda: "Dude, really? That's all you got?" The only bigger arcs with a slightly different structure are WCI and Egghead and here Oda hilariously enough took the WCI structure and made a carbon-copy to use it for Egghead again. So he has exactly two formulas he can work with for bigger arcs. That's just really disappointing.
3) Character writing and interaction in general. Pre-skip it was actually pretty fine, post-skip has been a bloody mess though. My God has it been bad post-skip. Not a single Strawhat had any kind of significant development post-skip, neither has the dynamic between them (only exception Luffy and Sanji on WCI to a degree). Nothing at all. Some characters have actually regressed (Chopper the main culprit). When I recently read the new HxH the difference between Togashi and Oda in terms of character writing was gigantic. Togashi can give some side-characters (Borksen, Morena) more personality in three chapters than Oda did with the entirety of the SHs in the last 600+ chapters.
4) Don't try to freestyle the final part of each arc. There has been a pattern in almost all post-skip arcs: They start of decently, sometimes even great. However, once we get to the climax Oda seems to freestyle and butchers any proper pacing this way. This way the overall arc gets dragged down pretty badly. Happened on Dressrosa (50+ chapters Birdcage fiasco), happened on WCI (30+ chapters of "weeeeddiiiiinggg caaaaakeeeee"), happened on Wano (70+ chapter raid and then a very abrupt ending) and on Egghead (20+ chapters for a speech that could've been done on two pages and a 100 yard run to escape).
5) Better fighting choreography. One Piece is a battle shonen, despite some fans trying to make it more than it actually is. Its fights are rather underwhelming though. Compared to other battle shonen, the choreography could be done much better.
