How accurately did Aoi Bungaku follow the original novels?
Aoi Bungaku is an ambitious anime and follows each novel closely. Madhouse took each novel and made adaptations to fit a whole novel into just a few episodes, leaving out some plot elements and changing some parts entirely while retaining the authors message.

Kokoro is actually a three part novel, however the anime only focuses on the third part, "Sensei and His Testament". Unlike the novel they took away the narrator and told the story from the perspective of the sensei, which follows the original novel more closely, and also included a whole new story as told from K's point of view. There are also scenes that weren't in the novel such as those which focused on the relationship between K and Ojo. 

In The Spider's Thread the criminal's violent deeds is depicted in more detail and exaggerated a bit to show exactly how evil he was, however the main plot of the sort story retains its meaning.

Run Melos was also changed as they included a new story of the author himself, and told parallel stories which complimented each other, the story about Melos and a story about the author's own life.

In Hell screen they change the setting, the original novel focused on a painter committing brutal acts in order to depict an image of hell, while in the anime he is a rebel that defies his lord's wishes to paint a beautiful albeit false image of his kingdom and instead paints the ugly truth.