Great overview of the life and works of Carr. Greene is quite readable, and manages to make Carr's somewhat sad and kind of annoying life and opinions interesting. I'm pretty sure he considers Carr's wife to be a saint, and I think I agree.
Greene's even better when talking about Carr's books. He's perhaps a touch too nice to some of the late, awful ones (maybe he really didn't want to offend the family). And I just don't find even the "good" comic ones as amusing as he claims to. But he's perceptive and thorough about every one he discusses. He made me want to try again with some of the 50s mysteries and a few of the historicals. And I will return to those written during his best period (late 30s/early 40s).
Goes without saying that this is for Carr fans only. If you like realistic characters, and dislike Romanticism, G.K. Chesterton, or insanely complicated puzzles, don't read John Dickson Carr.