I bought this book many years ago, not long after I had seen the movie (which I liked a lot at the time, but only because I was about 11 or 12, and liked many things that I've since found to be...well, less than good).
It was cheap. The pages smelt nice. It fit nicely inside my coat pocket, should I have ever chosen to take it out on the go. (Appropriate, seeing as it IS a Pocket Book, after all.)
But was it any good?
As I recall, it was a pretty solid read. It was certainly one of the more well-written movie novelisations that I've ever read.
Even better, the novelisation vastly improves upon the film, filling in back stories, plot details and explanations for some of the supernatural elements that the film had seemingly forgotten to do. (e.g. The scene where Pruitt Taylor Vince was attacked? In the film, that whole bit seemed a bit murky, details wise. In the book, I believe that it changes the circumstances of the attack slightly, thereby making it more clear what happened.)
The plot in general is still absolute bobbins, and no amount of screen-to-page improvement upon the film can change that.
I've heard time and time again that the original "Hellblazer" comics that "Constantine" is based on are much much better than the film, and I don't doubt it.
But out of all the things that came out of the film adaptation, this novelisation is probably the best of them all...