Although branded mystery stories, there's usually very little in the way of mystery in any of the books, and what there is, is easily worked out. What is enjoyable about these books is their gentleness, and the quiet interplay of the characters within them. They can be a bit twee, but they're enjoyable when you don't want your brain to be doing too much work.
The fourth in the series The Careful Use of Compliments v. 4 (Sunday Philosophy Club) continues to follow the lives of the philospher, Isabel Dalhousie, and her lover Jamie, with a new addition to the family, their young son, Charlie. Although there is conflict within the novel, everything resolves happily with even the most unpleasant characters appearing to have had a change of heart. Sometimes, this series can be mildly irritating, real life is rarely as happy and untouched as the life that Isabel leads, but sometimes you rather wish it was, that I think is the real charm and appeal of these books.