Yep, very different in tone and content to the TV series, the first one is about the ice-pick killer. Yet the main plot thing was whether Dexter was actually the murderer himself, which they obviously couldn't do in the Tv show. As it's first person, you don't find out much about other characters, and it all starts to get a bit supernatural in later ones.
Personally think this Dexter is a lot geekier, but thinks he's cool, in the end Hall's portrayal of him took that aspect out of it, because he's a dude.
Interesting, but as I say after the first book, very little to do with the series, more broadly comedic too.