So, yeah, Harry's dead. (Sort of. Anyways, he's not properly alive.) That's why it's a ghost story.
First, I've noticed that the tone is different in this novel. It seems like Harry is spending a lot more time inside his own head in this one, which I guess is a reflection of his state of being...not exactly alive.
This change of tone reminds me of Proven Guilty when Harry wound up acquiring an apprentice. It's entirely different, but they remind me of each other because they're both a change of mindset. In this one Harry is basically existing as a set of memories (or anyways a ghost does, I'm guessing it's a similar thing since he's just his soul, according to Bob...?) whereas in Proven Guilty Harry is having to change his mode of thinking to accommodate an apprentice. Either way, a change in mindset.
The other thing I noticed, Harry hasn't once oggled an attractive woman in Ghost Story. Which is unusual, since he's a pretty horny man. But then again, it's not so surprising when you consider that he doesn't have his body in this one. Therefore, no pesky hormones to distract him from work. The really funny thing is that he hasn't noticed this detail for himself yet.