MacCullouch already has written a very well respected book on the Reformation (800 pages by itself). And frankly there is not much to say about the reformation that someone else has not already said several times. (Although that is probably true about this whole book.)
The reformation (and counter-reformation) really are very important to the later history of the church. As MacCulloch points out several times, there are ramifications that still play out in modern politics and religious life. So it is reasonable that he spends a lot of time talking about the reformation. But it get a bit dry.
I think I will keep listening but probably will not post again until the 19th century is well under way.