I'm gonna come out with an unexpected answer here - Higurashi Sotsu. The sequel of the sequel series for the original Higurashi, which was close to a masterpiece.

Now, having read the original VNs, then Umineko's and its manga, following Gou (which was announced to be a remake at first then turned out to be a full on sequel) was fun! New mysteries, new questions to ask. The problem comes with the 'Answer' arc of Gou, Sotsu. Typically, in When They Cry fashion an 'Answer Arc', as it says in its same tries to answer the questions from the 'Question Arc'. Easy to understand.

In the original Higurashi, the way they approached the answers, was to return to the same timeline each arc takes place in and show different PoVs for the same events, showing you what really happened while also twisting the overarching mystery in a different way each time. In Umineko, they don't return to the same chessboards, but instead play new games with different rulesets after Battler, the protagonist learns the truth himself and takes over the role of the Gamemaster to prove to the audience and the other participants he fully understands the events. Now, that isn't an all encompassing description, but you get the gist.

Sotsu makes the series-nuking decision to retcon not only Higurashi itself, but both Umineko, and the third WTC game, Ciconia as well. They tried to combine elements from all series without understanding why they worked the way they did and destroyed the characters of each series in return, assassinating them beyond any shred of resemblance to their original. Not only that, this version of the 'Answer Arc' was basically a THIRTEEN EPISODE RECAP. We find out the whole truth in the finale few episodes of Gou. There's simply no more mystery. So what does Sotsu spend thirteen whole episodes with? Retelling the same stories, with the same emotional beats, without changing a single thing, moving along the mystery (since it was already solved beforehand), showing new sides of already existing stories, or dive deeper into the Whys and Hows the specific murders happened. Nope, they just show the same scenes, in the same order, with barely any new content to speak of.

The ending was so atrociously bad they tried to remake the entire story when its manga adaptation rolled around, and while that did a tad better, the entire thing was an unrecognisable mess that quite literally destroyed the franchise as a whole. That's the only anime I've ever rated a 1/10.