Just finished this one. It was very good, but not but not as good as Night Watch imo.
A few observations:
A .E. Pessimal was great. I actually thought that sending him to Vimes was a typical Vetinari plan, so he would end up joining the Watch and getting Vimes to deal with some paperwork properly.
Angua was annoying, as swreader mentioned, and a bit of a bitch I thought, no pun intended. Tony, you said that you thought Terry likes writing for Angua, which I thought was funny because I got the opposite impression. Most of what we hear about her in this book is to do with the werewolf/vampire thing, and how she is pleased to hear about Carrot's heart beating faster, but this to me came across in a possessive, rather unemotional way. We don't seem to get any expression of her love for Carrot, or what really makes her tick as a person. I've always found her character to be lacking something to be honest. Maybe I missed something there, I don't know.
Also there is the bit where Angua sees Sally leave as the bats and decides not to tell Vimes, as he might just put it down to their rivalry, well this just doesn't make sense. She must know that Vimes would believe her after all this time.
Mr Shine should have made an appearance at Koom Valley, or at least met with Vimes later. He has the one very important meeting with Vimes, and then we don't see or hear from him for the rest of the book. I would have liked to have seen Cheery used more as well (is she a Sergeant by now? Surely she should be), especially as Detritus was great in this one.
And the whole Nobby/Tawnee business was just nonsense, sorry. I thought the girls' night out was a good idea in principle, but had the potential to be a lot better. And Vimes stopping the traffic to get home for 6 o'clock was a bit much for me as well.
It's starting to sound like I didn't like this one. Actually I enjoyed it very much, there is lots of action and it was very hard to put down (so I didn't, and read the last half of the book in one go), but there were just those few things that annoyed me.