Wano
-Retconned Luffy fruit from a simple paramecia to a mythical god fruit 1000 chapters in the manga, with little to no foreshadowing (all the issues one might have with current God Piece started there)
-Introduced Kaido's kid in the middle of the arc out of nowhere, have her become prominent character and claim she'll join the crew everytime she opens her mouth to change her mind one chapter before the end of the arc off-screen (I was actually skeptical of Yamato joining, but the way Oda did it was extremely rushed)
-Introduced the last admiral, that was teased since Dressrosa to have him leave 3 chapters later in a very anticlimatic to hype up Shanks and promote a movie
-Mama mode (somehow never hinted once in WCI although BM was surrounded with her children)
-Teased Zoro's background to do nothing with it
-Zoro's promise to visit Ryuma grave either forgotten or off-screened
-Since Zou the arc was building up to opening Wano borders... for it to turn out it wasn't the right time right at the end
-Every single smile turning out to be fodder trash
And that's just what I'm thinking of right now
Fuck Wano