I love Terry Pratchett, and every time a new book is announced I preorder it immediately and spend the follwing months alternately jumping up and down in excitement or worrying that it won't be as good as I expect...thankfully Snuff was worth looking forward to, hooray!
It is really dark...really dark...but it is a Vimes story and he does tend to attract violence, even when on holiday. As usual he makes you think about the way the world is, and the way people can be, in fact it is a much more serious book than earlier Discworld. It will still make you laugh though, and perhaps make you feel for the characters more than ever before. I think you can't just class the Discworld as 'comic fantasy' any more because the issues Terry Pratchett tackles are so real you actually forget that Goblins don't really exist.
My favourite aspect of it was Vimes's relationship with his son. I love that, as in Thud, he thinks that the most important thing in the world is to be home to read to Young Sam or listen to him read aloud, and really loved that everything he reads has led him to a passion for poo. When I was telling my Dad that loads of kids books at the moment include poo he didn't believe me, but just put it into Amazon as a keyword and you'll see the range! The Story of the Little Mole who knew it was none of his Business is my favourite for sheer 'ick'ness, there's even a plop-up version available.
The action scenes are exciting, the dialogue is witty, the relationships are great...to cut a long story short, read it!