everything but: equal rites, pyramids!, sourcery, and (arguably) color of magic/the light fantastic. the first three are pretty sloppy and lazy; the latter two are his first discworld books where he was trying too hard to be "fantasy" douglas adams.
mort is a love it or hate it book; i hated it, but it was pretty polished and original for one of his early books.
given how prolific he was -- 70+ books in 66 years of life -- he has a remarkable lack of klunkers.