Not just Terry Pratchett. Ben Aaronovitch once said (regarding a Doctor Who New Adventures novel of his), "I'd like to remind everyone that while talent borrows and genius steals, New Adventure writers get it off the back of a lorry, no questions asked."
Since Gaiman wrote a book with Terry Pratchett--the marvelous Good Omens--I wonder if people on these boards have read Gaiman's other stuff. American Gods, in particular is my favorite novel.
I read American Gods earlier this year and was drawn straight in. Because I was such a huge Greek Mythology nerd, I recognized a lot of the characters in the beginning but that didn't take away from the book. A lot of it is just so intensely thought provoking, it's easily on my top 50.
Its ne of my favourites as well. The follow on is quite good as well , Anansi Boys .Its more African Mythology so you're less likely to know all the background with a greek myth background
There's also a short story called 'Monarch of the Glen' in Smoke and Mirrors which follows Shadow after American Gods
The only stuff I've read from Gaiman so far (watching the beautiful Coraline movie aside) is his fascinating Marvel 1602 series. Found it randomly during a sale on Comixology.com, and it's a really cool short alternate universe series for the Marvel supers (X-Men and all!)