Worst writing, by far, was the Kin Gin Bros fight.
I'd also throw in Chouji's whole struggle to punch Edo Asuma... that hesitation was just obnoxious; I feel like it forced Chouji to repeat the growth he'd already experienced in the series (if there's a pun in there, it was not intentional).
I hated the writing at the start of Part 2. The plot was slow, Naruto consistently came off as a weak, clueless idiot, and Sai was the most annoying character ever introduced.
I'd also argue that Kage Summit Arc Sasuke was hard to watch. He was badass at times, but he just got too crazy. Nothing Sasuke did made any sense, and that impulsiveness didn't fit with his previous character. Kishi did a good job bringing Sasuke back down to "Sasuke" levels of crazy when Sasuke re-entered the Manga during the War Arc.
I also hated Hebi Sasuke's writing, so I really didn't like Sasuke again until very late into Part 2.
And yeah, I'd agree that the writing in The Last feels terrible. The characters don't seem in-character; they seem like cliche characters from other animes.
