Finally, a key to the keys!
A recurring frustration for this Bachphile has been the lack of CD notes - apart from the older Rilling recordings - letting me know the keys of the different movements of the different Bach cantatas. For example, it is extremely important to me that the Cantata 4 - "Christ lay in the snares of death and has given Himelf for our sins" - has all eight movements in E minor. The B minor Mass Crucifixus is likewise in E minor, and it helps me a lot to know that identity of key between the two works. The Durr book gives us not only the keys of all movements but also the time signatures.
The structure of the book is extremely accessible and invites browsing. Each cantata gets about five or six pages. A real pleasure is to listen to the cantata and read along, noting text, key, and time signature.