I read the Ghost Map on the weekend. It was quite enjoyable. I'd heard the outline of the story before. I've read and seen reports on the London sewers and they normally at least mention the London cholera outbreaks and the way in which it was first linked to water transmission instead of Miasma. This was a much more thorough coverage of the events.
It was a good read too - I knew the ending and yet I didn't want to put it down.
I was struck by a few points - one of my favorites being infant mortality dropping due to a rise in tea drinking.
I went to the site about John Snow maintained at UCLA which is mentioned in the Ghost Map's references. Lots of cool stuff there.