A novel (this is what one needs to take into the consideration not to mistake the book for the real memoir!) about the psychiatrist in personal crisis and a wise guardian angel to guide him to the better understanding of the spiritual life.

Mixed feelings here. The concept is interesting and a lot of insights is spot-on (actually some of them were what I truly needed to read!). My spiritual life will be better (or I hope to, knowing my undisciplined self :)) after reading this book.
Yet - from time to time I felt that Kathleen, the guardian angel, is limited to the role of a "guru" of sorts. While her advice is (mostly) sound and her presence comforting, the role of the guardian angel is bigger than just being an adviser: the role of the guardian angel is both to guide us to good thoughts, works and words, and to preserve us from evil.
I also have some minor theological differences/questions (like how we know that the one guardian angel serves to more humans? And so on. I understand that the dispute is open here, but I like to think that I am the long-time and only "job" in my lifetime for my angel (I certainly need that much care!)).
I would also love to see much more emphasize on the sacramental life (namely Penance and Reconciliation and Eucharist). They are so important!

Having said all that, I think the concept of the book serves to people with certain questions and issues (like the ones concerning the deepening of the spiritual life) and the author has aimed the book for this type of questions. I have certainly been enriched there, and for that, I am thankful.
I recommend to read more books from various authors about the subjects, there is a lot of them of great quality. Therese de Lisieux comes to mind here.