I'm starting to find Adam Dalgliesh mysteries a little depressing. Murder mysteries in general dwell on the worst aspects of human nature. The pleasure in them that I can see is following the logical process that pieces the clues together and uncovers the truth. Dalgliesh doesn't seem to enjoy his work and he has intuitive hunches that are usually not shared with the reader. I suppose the reason I prefer Science Fiction to Mystery is that SF is the most optimistic of genres. Even the darkest dystopias are about fixing the problem, or at least about warning society about the potential consequences of current political, economic, religious, scientific, or sociological trends.
Yes, I just reviewed a Mystery novel by talking about how great Science Fiction is. I'm sure all of P. D. James' fans will appreciate it.