Just finished this, bought for a pound so may be this has some influence on my conclusions (joking)
Im aware of the bad reviews on amazon: yes the plot is a bit foggy (irony), some characters a bit flat and the protagonist - well hard to like.
However, i thought this was a great book .... alot of the bad reviews i sum up to: not liking the descriptions of gore, violence, darkness, debauchery or opium. If not read in a short space of time, the fragmented, allusive, short chapters could easily confuse and negate the really important assumptions/questions needed for the story to progress as the author intended.
I actually thought the ending was fitting, historically interesting and justifiably different to the whole book, yet this was the main criticism on most review.
Do not be put off