In the first book, Perry was straightforward and to the point. In Sleeping Dogs, it's almost as if Perry was told by someone that you have to explain every detail of every character. This includes people who are just about to be killed. So with every new character he brings in, we get a few pages of history on the person, only to have them get killed a second later, or leave the plot line never to be heard from again.
The ending was a real disappointment. The method Perry uses to allow The Butcher's Boy to get away is very poor. I really felt cheated.
So my advice is read the first one, and skip the second.