I am team teaching the Jr./Sr. high Sunday School class in our church and we have been using this series for about a year. We have really enjoyed Max Lucado's insight into the various books of the Bible we have studied.
We are studying this book in our small group. Our group is made of mature believers who are regularly studying the Bible on their on and for many years. As a leader, I find that this book does not go as "in depth" as I would have liked. I find that I am adding questions that dig deeper. It explores mostly about how the passages pertain to our life but has little study about the life of the Corinthians and the things that were happening during their time and why Paul needed to write this letter to them. Personally, I enjoy a study that can explore both. All in all, I think this would be a good book if you don't want to go too "in depth" and is a decent starting point for people who do.
I am getting very good use out of this study guide. The only disappointing thing is the fact that the author did not cover chapters 5 through 8 for this study. Most people who are new at studying God's word, would appreciate views on all chapters.