I own, and have read, every book he has written. He has a new Davenport novel out now, "Field of Prey." A new Flowers novel is due out in the fall.
While I will still buy and read his books, I think the quality of the more recent books is slipping a bit. I liked the earlier Davenport novels much better...when he was single. There is a reason that in most crime fiction, the main character is single: it gives him a great deal more latitude to interact with females (witnesses, suspects, fellow officers, and other assorted women) he comes into contact with, and Davenport was "active" in that regard, when he was single. Also, a single man doesn't have home and family obligations to worry about...so he can concentrate on investigation, travel, etc. I know that he is aging as we all do, but this is fiction, and in fiction he doesn't have to settle down and get older!
I find the Letty character annoying...while she was much less so when initially introduced, she has become (IMO) a strong-willed smart-aleck with a foul mouth, which I wouldn't tolerate from my daughter. Also, I find the latest book's use of her actively taking part in some of the investigation as ridiculous.
Virgil Flowers is a much different character than Lucas Davenport, and at first, I wasn't too sure about him...but over the course of several books, I've found I enjoy reading the later Flowers series better than the later Prey/Davenport series, since Lucas has become such a different character. I miss the fighting, frolicking, and hard-charging Lucas of the early books.
Still, with all the criticisms I've mentioned, I like Sandford's books better than anything else I've come across in the genre. I like Lee Child, too, but sometimes his Jack Reacher character is a bit extreme.