if you want a social history of the Catholic church immediate post-V2 in a typical American rust belt town, this is your series. The series is set in Detroit and gives an insiders view of the day to day workings in average parishes and sometimes in the local hierarchy. One book is set in the seminary for instance. All the stories involve mysteries of course but the backdrop is always the pastoral problems any priest faces and the diversity of human sinfulness. The pastor who is also the amateur detective adheres to church teaching and discipline but is not a traditionalist by any means. When he dissents he keeps it personal and does not preach or act on his inward doubts.
The details of canon law, church governance, pastoral practice etc. are spot on, as are the character studies. No there is nothing against the Church and Fr. Koessler is not as dissident as Andrew Greeley’s priest detective, but the full spectrum of misbehavior (clerical and lay) and cavalier attitudes toward doctrine and clerical discipline are part of the plots. It is interesting that the first book, Rosary Murders, set I think in early 70s, deals with a penitent who confesses abusing his own child. He also avoids graphic sexual details although that type of misdemeanor plays a solid part as you would expect in any mystery series.
While all the plots have a church backdrop and clerical characters, there are plenty that deal with lay Catholics behaving badly as well. No he does not write with deliberate criticism of the Church (as Greeley often does), but is honest about the full range of human sin that Catholics fall into. The books deal with the full range of problems and issues facing Catholics, lay and cleric, in the 30 year period after the Council.