I'm late to the party on this - several years, in fact - but I'll still throw my oar in
I agree with the post upthread that called this 'interesting but frustrating'. It and Equal Rites are the first *true* Discworld novels, I think. There's a tangible atmosphere and style to them that the first two lacked. It has more of a sense of place.
I'm also a big fan of the scene between Mort and the old woman. It's one of my favourite Pratchett scenes period although a lot of them feature the Grim Reaper in some shape or form. (As an aside, I've just finished Maskerade and the scene between Death and Granny, involving the cow and the baby, is the highlight of a fantastic book)
The ending really does need a lot of work, doesn't it? I feel the series is still a few books away from his mastery of plot and some epic endings. I don't really know what is going on. I hadn't spotted the SM retcon mentioned above though - that's a cool though, although I have real problems with Soul Music as well (I feel it's his weakest book after Sourcery. SUCH a missed opportunity).
I've a lot of love for Mort though. It was one of the first of his books that I read and I loved going back to it a few months ago. I've written more about it here
, if you fancy something to read over a cuppa this morning