A day later: I didn't comment right away, partly because I was miffed to have the rest postponed (but which I now find great because it means more happy next Saturday, and I can think slowly about the first part); and partly because my nephew was visiting and we found Star Trek Voyager (which he hadn't yet seen) on another channel.
So: Characters convincing? Yes. Although Vetinari is physically darker in my imagination, his character was well done. Mr Groat's odour and self-medication didn't seem to be conveyed. Plot faithful? yes. Does the essence of Ankh Morpork transmit to non-AM-readers? Now how could I possibly know that?