"Bonhoeffer & King: Speaking Truth to Power" by J. Deotis Roberts was a book with an interesting concept: lay the lives and thought of Dietrich Bonhoeffer and MLK side by side to show all of the various ways in which they were moving in the same direction. While I found the concept intriguing, I thought that the book left a lot to be desired. I felt that the author did not put very many original thoughts into the writing. In my opinion, he merely copied and pasted together correlating information from the biographies and theological writings of the two subjects.
Part of my struggle with the book is probably due to the fact that I took an entire class in seminary on Martin Luther King. This book was pretty short (130 pages) and did not go into any sort of depth, so I really did not learn anything new about MLK. However, it was worth reading for me to learn some interesting aspects of Bonhoeffer's biography, of whom I am not as familiar with as King.
If you are unfamiliar with Bonhoeffer or King (or both), this book would make for an excellent primer. If you have studied either one before, you will likely be pretty bored with the book.