I might as well throw my two-cents in.
First I'll get the complaining part out of the way: The Sally and Angua bar scene dragged and didn't really have any conclusion. It just sort of petered off. While I think that it's interesting that Carrot's over-dedication to his job may end up ruining his relationship with Angua I get the feeling that this'll never be brought up again. Also, Sally is annoying. Yes, I realize that she's annoying because she spends most of the book hanging out with a werewolf but maybe it would've been a good idea to see more of how she acts without Angua around. I don't think this will happen, too, because Pratchett seems to be going for a "Hyper Police" thing with the two.
With that said, I really like this book. I like how awesome Vimes is throughout, I like Angua, I like Detritus and I like Carrot (even though he's barely in it). I still say this book should have been called Vimes is an Awesome Bad***.
I'd say this book is more about racism in general but there is some commentary on religion here and there (most of which I didn't care about). I don't really think religion as a whole is portrayed as good or evil here. I mean, yeah, we have a group of dwarves willing to destroy history for the sake of not liking it but it's also balanced out by Mr. Hand-For-An-Axe (yeah...I forgot his name since I read it). If this is an anti-religion book then...I'm okay with that. At the end of the day there are bad things to be pointed out about almost anything, so why not? At least it can still be enjoyed for its story and characters if you don't like the message.
As for the lack of jokes everyone keeps talking about I honestly didn't mind.