Maybe it's because I grew up with detectives like Columbo and Nero Wolfe, but I tend to like my heroes to have the occasional flaw. Lucas Davenport is a tough and experienced cop who doesn't play by the rules. He also has rugged good looks and an animal magnatism that allows him to bed almost every woman he meets (except stupid girls and the nun with the skin problem, so I guess that proves he has standards). But he also has a sensitive side, as he enjoys reading poetry on the sly. And he's a genius, a popular game designer, which means he's also wealthy. Wow, this guy is good at everything. How boring. He's the kind of character I would expect a sexually frustrated high-school student to create.
Now let's add a serial killer into the mix, but make him a socially inept loser who is inferior to our man Davenport in every way imagineable (oh, he's clever, but not as clever as Lucas), and you have two main characters that you really don't care to read about.
Sanford has a habit of making even supporting characters appear shabby, incompetent and unappealing around Davenport (including TWO pairs of Fat Cop and Skinny Cop duos), and has him so on top of everybody else that he has to advise the Chief of Police how to handle the Media and information control (don't the police have people to handle that?).
Finally, Sanford proves repeatedly that he knows little about police procedure or the historical crimes he references (newsflash: David Berkowitz was not the lone killer in the Son of Sam case, and he wasn't caught because a cop looked in his apartment window and saw copies of the letters. He lived on the second floor, you see...). I can only assume by the success of the Prey series the books have improved. Actually, I can only hope.