A friend lent me 'In a Dry Season' (10th in the series) and I enjoyed the book; liked the detective, Alan Banks, and wanted to find out more about him so started at the beginning. I've read most of them now and, with the odd exception, have loved them. I did find that the stories became darker as the series progressed.
I'm so pleased that I didn't see the TV version, 'DCI Banks' first or I may never have read the books!