This is one of the Great Courses available on Audible. It is a survey of mystics within the three major monotheistic religions. It would be a great introduction to the subject. Each unit is thorough, well researched, and well presented. Unlike many of the other professors/narrators, Luke Johnson is worth listening to and is an asset rather than a liability for this title.
That said, this was an overall disappointment for me. I am already quite familiar with the desert fathers and medieval Christian mystics and because this course covered such a broad range of characters, I learned little new at my point of greatest interest. Also, the fact that so many individuals were covered, created two serious flaws. The first is that the thoroughness of including so many people pretty much guaranteed that there would be no real depth at any one point. I would much rather have listened to a course that touched on a third as many people (or fewer) but went into three times more detail on what they believed, wrote, or practiced. In my opinion, this would be a to truly get a grasp on the mystical tradition. The second flaw in the number of individuals covered was that Johnson included many people that I would not even begin to consider mystics. Some examples would be Calvin and Luther from the Christian tradition and Al-Ghazali from Islam. Although all three might have tangentially written some things that might have been loosely drawn from previous mystics, they certainly were not such themselves and certainly did not contribute anything to the mystic tradition that was not better said or understood elsewhere. Johnson also included Sabbati Zevi, and though you cannot have such a course without him, I believe, and most would probably agree, he should be viewed more as a charlatan posing as a mystic than as a mystic in his own right.
Another complaint is a common one I find when listening to or reading from liberal Christians when writing about Islam. One can either be kind or accurate but not both. Most liberal scholars try their hardest to be kind, but this can only be accomplished by careful cherry-picking of the truth. Any factual analysis of the earliest days of Islam (the lives of Muhammad and his earliest followers) and the early writings (the Quran and hadiths) will almost certainly get the scholar labeled an Islamaphobe. There are many decent and noble people within Islam. Muhammad is certainly not one of them. There are many brilliant and beautiful writings that sprang out of the Islamic tradition. The Quran is certainly not one of them. Anyone who doubts either of these two statements is either hiding the truth or ignorant of it.