I have heard of Terry Pratchett's Discword series, but had never read them until now. In the airport Borders, I picked up Thud! and bought it purely based on the fact that my friend, Belsum, enjoyed it and the rest of the series. I didn't get to read it until I got home, but I just finished it and enjoyed it thoroughly.
The best thing about it is that even though it's a late book in the series, it's pretty much stand alone (I understand that most if not all of them are). I could enjoy the murder mystery "A" plotline and follow (slightly vicariously) the character development of the recurring characters.
The characters are the second best part. They are funny and well-rounded and, most importantly, engaging. I would love to follow the story arc of The Watch and plan to use the handy chart in the Discword wikipedia article to do so.
I could go on. There were lots of lovely bits of writing, though Prachett was occasionally heavy handed with the parody (the "accent" for the troll mobster comes to mind) and overall it was a light and easy to read murder-mystery... set in a fantasy world with dwarves and trolls and magic, etc.
Delightful and recommended.