I have seen the musical film, and I didn't like it. But is heard good things about the book...  The investigative way it's written draws you in, it's creepy and cool and you wonder how can this ghost be real?! 
And in the end it's so bizarre and farfetched. I would occasionally get confused about who was who, or who was speaking, what a shame it didn't end up being a 5 for me!