These are different stories involving Devilman's world. Some are about Devilman and add to the mythology some are separate stories that don't involve Devilman but take place the same time as the events in the original Devilman manga.
Right when I finished reading the original Devilman manga, I knew I needed more of it, and what better way to get more than to read a collection of stories entirely focused on the Devilman universe. Although different with each story, each does its own to add to the series. Story- There is a total of eighteen stories, each done by different authors with their own unique takes on Devilman and the series itself. They are either about Devilman himself, or are about seperate stories that don't involve Devilman but take place during the original Devilman manga. Obviously there are going to be stories that'll leave a bigger impact than others. One of my personal favorites has to be the one about Miki's necklace, with the emotional impact. But everyone is going to have their personal favorites, the question is whether the reader is already familiar with Devilman. Art- Because of the different authors, the artstyle is always going to be different with each story. Some of course will be more fitting to the overall tone of Devilman, but I think its interesting to see some of the old artstyles some of the authors have. Adds variety to the stories. Characters- Some of the more familiar characters will be making appearances here and there, but there will be stories with their own characters. There's the story of the girl who has a secret crush on Akira, a boy who sees society and his own family fall apart around him, and others. There were characters that left more of an impact on me than others. But I feel like these stories are best read at your own pace. Overall- The ideal short story series for anyone who happens to love Devilman. While not every story is a masterpiece, they overall carry the same themes as the original Devilman, making them somewhat memoriable. The ideal short series to read on a day you need some Devilman awesomeness!