thepunktheory
First of all, only the first season of the show and the first novel share (more or less) the same plotline. I was surprised to find out that after that they go different ways as there are 8 novels and 8 seasons.
So, I'll begin with show. Dexter was already famous, had reached it's peak, had 8 season and was cancelled for quite some time when I finally got started with the first season.
Well, I discovered that Dexter is a rather unique character. You can't decide whether he is good or bad but not matter what you'll end up liking him. You get a very good insight in his mind and what drives him but the other characters are also portrayed very well and rather deeply. Furthermore, the whole new serial killer aspect was introduced extremely credibly. I don't know about police work but the way everything is depicted in the show, I would believe it in a heartbeat.
So, let's move on to the book! I was really excited to finally read Darkly Dreaming Dexter. Unfortunately I ended up disappointed.
First of all the storyline. The novel is only a little over 300 pages. That's not much if you want to portray Dexter, show his troubles, depict how he kills, then introduce a new serial killer, and catch up with that guy. Thus, the whole story seem rather rushed. Lindsay has a way of jumping from one point to the other in a way that made me wonder whether I jumped a chapter or two. Thus, the book was not nearly as credible as the show.
Another point is the character depth. As the novel is rather short, Lindsay ha trouble enough to give his main character Dexter adequate time to unfold. Unfortunately most of the other characters fall by the wayside and remain totally pale.
But what annoyed me most is the ending. I don't want to put any spoilers in the text but as it turns out, the endings of the first season and the first novel differ. This wouldn't be a problem if both of them seemed credible. However, the ending of the book is rather irritating and doesn't really make sense. In some way it also lacks depth, especially when it comes to other characters.
Summing up I have to say I'm super disappointed by the novel. The TV show is so much better, I was really surprised. The book isn't really worth reading. It's not even enthralling, whereas the show makes you want to watch every single episode in a row.