•Why it earns a slot
Why it earns a slot: it's the book where Conan Doyle, tired of the character, applies Holmes's own cold logic to killing him off at Reichenbach Falls, ending the collection with the detective's death instead of another solved case.
Twelve cases where Holmes is right about almost everything, capped by Arthur Conan Doyle throwing him off a cliff to be done with him.
This distillation is written from the freely available original, which is always the better read when you have the time: Project Gutenberg.