Jujutsu Kaisen
This might be a strong take to start off with but I feel like Gege Akutami should be required to give half of the credit for JJK to Kubo Tite, Masashi Kishimoto, and Studio Mappa as it feels like its strong start was owed largely to them and it felt like he had no idea what he was doing after Shibuya.
I, like many others, was introduced to JJK through the anime adaptation and there was a lot to love at the start. Although many of the elements of the series were very reminiscent of series like Bleach, YuYu Hakusho, and Naruto, the execution of these tropes and characters were fresh and it felt like JJK had figured out the formula for modern Shonen. Unfortunately, this did not remain the standard, because the story eventually became bogged down by subplots that never were resolved, characters who never paid off to anything, and the pacing and questionable story decisions in the second half of the series were actively were a detriment to my enjoyment of the series.
There are a number of characters that die suddenly after either being present or hyped up for large portions of the story. A certain important character is hyped up, but immediately loses their first onscreen battle due to their opponent somehow having the perfect counter to their powers despite never alluding to that. However, the more infamous of these events in the story is chapter 236, where a fan favorite character seems to be winning a fight, but then proceeds to get absolutely hoed off screen just because it generates shock value. I would not even have been mad at the result, but there was no explanation for why it was done the way it was. Normally, the rule of storytelling is "show, don't tell", but for some reason the author loves to "don't show, and only tell 20 chapters later". He built up characters as being arrogant and confident on screen for hundreds of chapters, but then flashed back to them being very vulnerable off screen only after they die. This leads to the "fraud" syndrome that is running rampant in the fandom, and also feels a bit like character assassination after the fact.
Other issues included walls of text, powers not really making that much sense (even for a Shonen series), oh and also killing off half the cast in Shibuya. Although there are interesting characters afterwards, the fact that JJK has such a strong start actually worked against it in the long run since I felt no incentive to become attached to any of the characters afterwards and this was compounded by the lack of payoff for any of the characters in the end.
Apologies again for the rambling, but the tldr of it is that the first half of JJK is good, but the latter half felt like the weirdest mix of decisions that were only focused on shocking the viewer with obviously very little thought put into the story consequences. It makes me sad how frustrated I became with this series in the latter half of it, and although I feel that it was an objectively bad ending to the series, it almost feels like a mercy killing and I'm glad I don't have to blow up my friends phones about how frustrating JJK is anymore.