Schöne Zeiten - The Good Old Days in the English edition - is a collection of mostly uncommented documents and statements from Germans who witnessed or took an active part in the Holocaust.
Members of the Einsatzgruppen and the staff of the concentration camps are quoted as well as soldiers who only witnessed the mass murder by accident. Almost none of them feel any guilt and almost none of them question the thought that the Jews had to die. The most you can expect is that it shouldn't be done in such a cruel fashion. Others concentrate on how bad it made them feel to shoot hundreds of people. Most make it clear in their statements that they knew well they could refuse the order to shoot people without any real consequences and some did.
The most striking document is the diary of the physician and SS-member Johann Kremer written while living at Auschwitz. He writes about the wonderful food, how excited he is about the opportunities for medical research, about movies he saw and, just as casually, about witnessing Sonderaktionen (the murder of prisoners who were too sick or just to make more room) or having people killed to get his hands on specimens for his research.
The title of the book is taken from a page in the photo album of Kurt Franz that contains photos of Franz in Treblinka and of the zoo (!) at the camp, fondly remembered. The book also contains a number of photos taken by the Germans - it was illegal to photograph the shootings or the camps, but many people did it anyway and some even showed their photos at home. The photos are extremely graphic.
It's a book very much worth reading if you are interested in the Holocaust and how it was made possible. You won't get any analysis of interpretation of the historical facts, just the view of the involved parties and you're left to draw your own conclusions. It might be a good idea to have some sort of reference book on hand to better understand the background unless you're very knowledgeable about the Holocaust already. If you are, you will probably recognise some of the texts and photos because the book often is quoted in other works.