Hughes helped me learn what it is that I like in environmental history. Perlin brought some of these lessons to the fore, but after reading Hughes' work I might treat Perlin a bit more harshly. Let's go over the different successes within Pan's Travail . For starters, from the very first page of the preface, it is obvious that Hughes is a clear writer. I am not convinced that everyone tries to be a clear writer.
Clarity is related to the goal of speaking to a wide audience.
I think clarity is independent of intellectual rigorousness and sophisticaltion, but in my experience, many books that aim for a specific scholarly audience have no desire to be clear. A clear argument is one that is built up slowly and carefully from first principles. Hughes states at the beginning that his book is intended for a wide readership. Many authors say this. But Hughes means it.