I love Hammett, and I think Thompson has some valid insights, but I'm kind of disappointed with this book. But it depends. If I were a regular reader of "detective fiction" (i.e., if Hammett didn't happen to interest me intellectually, and if I read any other detective fiction with arbitrary delight), I might have actually loved this book. So don't base your judgment entirely on what I have to say about this book.
But what I will say is this: as a student of philosophy and English literature, and as someone who has read some literary criticism in his day, I will say this book is disappointing. Part of the problem is, Mr. Thompson tries to cover way too much. What I mean is this: he takes you through the novels entire. What he might have done is taken a more specific theme and found the places in the novels that fit with that theme. What you need, in that case, is not the entire novels: you need only "pieces" of each novel, and more speculation, more imagination. Not explication. The assumption should be that your reader is reading you because they've already read the author's books already.
For a good example of what I mean, read the Introduction to THE CONTINENTAL OP collection by Steven Marcus. His theory of the truth/fiction dichotomy in Hammett is very fruitful, and very short.
This book is advertised as "in-depth" and "influential." I don't know how influential it has been, as I have not read ALL the criticism on Hammett over the past forty years. But I really don't think it is "in-depth": it's more of an introduction.
There really is, I think, too much focus out there on "Hammett's Development As A Writer." To HELL with his "development"! He was a writer; that is all. There is no "development": everything he wrote was good. He might have changed over the years, sure. But it's not as though he started out as a hack writer and ended up as a brilliant novelist in the end. The fact of the matter is that Hammett was able to say in very few words what it takes other writers pages and pages and pages to say. It is simply more difficult to write something short than it is to write something long. This may be especially true of detective fiction. For instance, why is it that we have so little of Hammett and Chandler, but they are still considered the best? Whereas we have volume after volume of Parker, Spillane, Burke, Grafton, etc., and don't seem to be an "Influence" on anyone.
But by all means, if you want a good introduction to Hammett's worldview, or if you're a book collector, or if you are really unfamiliar with literary analysis, you might love this book.
But I wouldn't read a mediocre book on Hammett for the same reason I wouldn't read a mediocre book on Shakespeare or Aristotle.