Ingrid mentioned disliking this book. I've read a couple of others by Bruen but i haven't read anything by Starr. This book was hard to like (not impossible) because I think it was something of a lark for both authors. They seemed to have a lot of fun topping each other. When taken less seriously than most novels - when taken in the spirit of the lark that it is - I think it can be enjoyed. It took me a few chapters to get into that mode, but then it worked. Overall, I'd give the book a B, I think. I have a couple of Jason Starr novels to read. I'm thinking they may well both work better separately.
As for what this particular novel has to say about hard boiled novels in general, I don't think it says anything on that score. Frankly I think any genre (any writing) can lend itself to flat characters. Bruen's Jack Taylor novels are definitely hard boiled, but Taylor's a pretty well rounded character.