There are going to be some major spoilers after my synopsis, so if you're planning on reading the book, watch out for the big *SPOILERS* note. Avoid at will.
As fans know, Dexter Morgan is a complicated guy. In his life as Dear Devoted Dexter, he's preparing for his upcoming wedding with Rita. In his life as Dazed Daddy Dexter, he's busy trying to explain to his almost-stepchildren Astor and Cody that they need to wait on the mayhem -- that they need to learn to blend in with everyone else before they can become his mini Dark Darlings.
That would be enough for most people, right? But we're talking about Dexter, so now for The Big One: At a somewhat tame (from Dexter's point of view, of course -- blood spatter experts/vigilante serial killers have kind of seen it all, you know) crime scene, Dexter's Dark Passenger goes silent. And shortly thereafter, it disappears. Without his inner voice to guide him, he is unable to provide hints about the case to his sister, and he just feels... lost.
And then there's The Watcher.
Dexter -- the book series -- has totally jumped the shark. Remember the stupid midichlorians from the new, crappy Star Wars movies? Yeah. About halfway through Dexter in the Dark, I stomped into the living room and declared, "Arrrrgh! Jeff Lindsay TOTALLY pulled a George Lucas!" You know what? Explaining The Force diminished it. And the same goes for Dexter. Changing his Dark Passenger from a metaphor into a literal being diminished it and diminished Dexter.
Dexter went from being something special -- someone who was, in my eyes, broken and, yeah, sick, but able to make it work for him -- to just... a poor schlub who went through major trauma and became host to (and dependent on) the bastard child of an Old God. Yeah, you heard that right.
I can't believe I'm about to say this, but I like the show a whole lot better. I like the show a whole lot better. How often do you hear that?
I'm pretty sure I'm done with the books.
All of this isn't to say that I didn't like anything about the book. I loved the Astor and Cody storyline, and if anything convinces me to read the next book, it'll be my curiosity about them. But, at the moment, my horror at the midichlorian parallel coupled with the really unsatisfying, slapped together, possibly-written-in-fifteen-minutes-action-packed ending has me feeling Deeply Disappointed.