Tom Holt is much in a similar vein as Pratchett (even shared the same cover artist for a while) with his satirical takes on fantasy & fairy tale tropes.

Surprised no one has mentioned Robert Rankin, who has a darker view that Adams but is good at satirical takes, even though some of his works do feel dated since they were written for the contemporary audience of the publications time.

Diana Wynne Jones is also recommended, she was an influence on Pratchett to a degree. She picks apart a lot of fantasy tropes in her books. she was also a friend and teacher to Gaiman. Most people know her for the Ghibli adaptation of her book Howl’s Moving Castle.

Jasper Forrde has been described to me as like Adams but haven’t read his book yet.

and finally the Gormenghast series by Mervyn Peake, which was referenced a lot in the early Discworld novels.