Death Note is a popular answer, and I also agree that its ideal stopping point is…
Death Note
L’s death
Bocchi the Rock is another show that I felt would be at its best if it stopped at episode eight. If the upcoming compilation movie stops there, I may consider it superior to the TV series. It’s not unheard-of. Violet Evergarden’s film-length recap stopped at Episode 10.
I want to see more of Bocchi-chan's rock!
The title drop + roll credits is its peak and climax. I hoped its finale would be amazing. However, episode eight overshadowed episode 12. Everything after E8 felt like a lede for an S2.
What are yours?
I loved Clannad, but I do tend to enjoy slower shows quite a lot, I see clannad as a sort of protoype of Bunny Girl Senpai, they’re extremely similar if you think about it.
Afterstory is a totally different beast and more or less comes out of nowhere to hurt you, but only if you actually connected with the characters in S1.
The comparison to Bunny Girl Senpai is a really, really good one actually since they do have an extremely similar storytelling structure. I watched that show+movie just recently, so it is fresh in my mind. I think the main thing that kept me engaged with Bunny Girl as opposed to Clannad is the characters. I really enjoyed the characters in Bunny Girl whereas in Clannad, whenever certain characters showed up (iirc, mainly the guy friend that keeps challenging a girl to a fight), I just found it annoying and took me out of it.
I think there is a lot you could compare/contrast between these two shows and it is making me think critically about what made one work for me and the other very much not work. Thanks for the food for thought!