I wasn't especially expecting to like this book. The humour of inventing unrealistic characters and then putting them in a difficult position has always seemed contrived to me. But a sudden impulse hit me in Vienna airport last week, and I bought it. And I rather liked it. I must get more of the Susan Sto Helit sub-series - she is a great character.
OK, I wasn't really sure that the plot made total sense in the end. The means and motivation of the villains, and to a certain extent of Death, are not so well explained. But Pratchett has managed to pack an awful lot of layers of allusion about families, celebrations, belief and morality into the story - and I think he does it rather better than Neil Gaiman in American Gods. I've been having fun glancing through this list to see what references I missed.
Two bits I didn't miss were his nods to Arthur C Clarke - when Stibbons explains to the Archchancellor that his computer works by "sufficiently advanced magic", and then a bit later on a paraphrase of HAL 9000 when Hex announces, "I Am Fully Recovered And Enthusiastic About My Tasks". Clarke of course is famous for wanting to explore spirituality without invoking God. Pratchett here is invoking gods, and many of them, but I think Clarke would be comfortable with the result.
And of course the main point of reading a Pratchett book is for the humour. The "Blue Bird of Happiness" was a particularly great moment of bathos. And you can't beat one-liners like "I'm sure he wouldn't keep on eating them if they were addictive."