Rated 4 for being the last Pratchett book and for the book it would have been had he had time to finish it.
I have a rule about Pratchett. I don't read any of his recent books anymore. I only listen to them. Something about Stephen Briggs' narration helps hide any decline or sense that the books are just not up to him in his prime. And the unfinished nature of this book meant that I really needed the reminder that I was reading Pratchett. Except when I didn't. Except when he gets everything right about living and dying and saying goodbye and evil and good and just trying to do the best you can.
It's not a perfect book - as others have said, the subplots need polish. But it is pterry's goodbye and, in that way, it is fitting.