I'm trying not to be too fangirly here. I really want to squeal and say this is the greatest book ever. It probably isn't.
SPOILERS! Don't read.
So what's wrong with this book? Well. I don't like Sally. She's just not interesting. You could get away with her character if you stuck it in one of the Rincewind books or one of the standalone books that aren't about any established set of characters (Small Gods, Soul Music, Pyramids, etc) but the Watch books have some of the most brilliant, carefully developed characters in the series, you can't just shove Sally in with Angua and Cheery and Vimes and Carrot. Is she there solely to make Angua jealous? Or for the rather erotic shower scene and references to mud wrestling with Angua? (because lesbianism had to come in somewhere and Angua/Cheery just wouldn't be that hot. Though he already *dealt* with it in Monstrous Regiment)
Also, Vimes agrees to have a vampire in the Watch far too easily. At first I was able to overlook this - He knows his prejudice is illogical, and we know from Jingo how hard he tries to avoid prejudice and just be a good person. But I got the feeling this was one prejudice he was determined to cling to. He doesn't.
The vampire/werewolf thing? Even in The Fifth Elephant it's not that pronounced.
However. Baby Sam! 'Where's My Cow?'! This is quite possibly one of the most touching portrayals of fatherhood I've ever read. The scenes where he's trying to get home on time and the entire Watch helps him made me melt.And the Where's My ow shouty scene near the end.
Also, little touchs of character developement which simply do not exist in the earlier books. Colon's suggestion that a robbery was done by a troll is actually rather impressive (or I have descended to Colonesque levels of idiocy). Detritus' paternal feelings towards Brick. Detritus' maturity in handling the situation when Bunny cleans out the stables for the trolls.
Oh, and I loved Tawnee. It's rather comforting to think that the only reason one is asked out by pathetic men is that the others are too intimidated. Except, of course, that one is not a six ft tall stripper with a perfect body. *sigh*. The thought of Nobby getting some is...disturbing, but it's at least relatively safe from fanfic writers.
It's getting harder and better to read Discworld books, what with issues coming in. Things like Vimes' grudging acceptance of technology are comforting in their familiarity, but Dwarf fundamentalism, gang wars, racism, etc are disturbing for the same reason. I often pick up one of the earlier books in the series for *light* reading, as opposed to serious, makesyouthink literature. I can no longer do that. And I love it. I love that he hasn't let the lightness of the earlier books restrict the potential of the later ones. Thud! is funny and silly, but it's also deeply worrying, and I think that is a major achievement. It's hard for me to be objective about Pratchett, but I'd certainly rank Thud! among the best books of this year.