The author's published material is very well known (and appreciated); in a positive and paradoxical sense, "there's nothing new under the sun". The content is

The author's published material is very well known (and appreciated); in a positive and paradoxical sense, "there's nothing new under the sun". The content is also extremely technical. I don't think in itself is "easy" to comment (at least, not in early stages). What's new, in a negative and surprising sense, is how little the author is profiting from the books.