I picked this up in a bookshop thinking it might be something like Sherlock Holmes, and in fact there's a quoute on the first pages from Sir Arthur Conan Doyle saying, basically, that he took his ideas from Edgar Allen Poe. That sold it to me because I like Poe even more than I like the Sherlock Holmes stories.
This book isn't exactly like either of those writers though. It has the clever solutions of Holmes (there's a great bit where a man is killed inside a locked room) and it has some of the weird darkness of Poe (the first chapter is especially unnerving). The effect, I suppose, is like watching a modern film in the style of those Victorian writers, directed by Terry Gilliam or maybe Tim Burton. A lot of the scenes are very visual.
There are some great characters and the story moves quickly, but for me the best bits were the scenes of Victorian London. Sometimes it feels like you can almost smell the place, and the final scene in the balloons is really atmospheric.
If I have one criticism, it's that I'd like to know more about the main characters- where they came from and where they are going to. I think this could easily be the first book in a series - it feels like a lot more can happen - so perhaps I'll find out more later. If you like old-style detective books or Victorian history, this is a good read.