Dexter, the new TV series, not the cartoon, is about a serial killer working as a bloodspatter analyst for the Miami Metropolitan Police Department. He grew up with a father who realized what he was, and taught him a code, so he'd never get caught, and would only kill killers.
If that doesn't entice you, what other reasons do you have to watch Dexter:
1. It has some of the best writing I've ever seen in a tv series. The dialogue is simply amazing. The series is full of vibrant characters, and it seems the writers really have a grasp on how to write characters of different intelligence. Most notably the police department has writing good enough to create real, living persons, while at the same time making them interesting.
2. Dexter himself, a character who thinks one thing (in voice-over, of course), and says the opposite. He's supposedly the most realistic portrayal of a psychopath in a tv series, and he's awesome. Michael C Hall earned a Golden Globe and a Screen Actors Guild Award, both for this role, and you'll see why.
3. Plot. It's based on a series of books, which means that seasons have themes, that there is overarching character development. The writers, if fired, are replaced with equally competent people who know exactly where the series is going, instead of just faffing about *cough*Lost*coughcough*. We get long stories, and every season ends with the beginning of the next one, in a smooth transition, so it doesn't feel as though the writers had to come up with something new in between seasons.
4. Cinematography. It's got good cinematography. It's not spectacular, but it doesn't have to be, as it focusses on characters and dialogue. Most scenes are shot in such a way as not to draw attention to the camera, but whenever there is action going on, such as Dexters own murders, there is quick, snappy editing, strange shots, most of them to slightly distance the viewer from the out-of-this-world mind of the protagonist. The strange thing is that action is not always where you would expect it to be, like in the opening sequence, which shows nothing but Dexter getting up, getting dressed, and having breakfast. And it's one of the most violent opening sequences I've seen in a while.
It's definitely a series worth watching. If you can, give it a try. Amazing cast, amazing writing, awesome plot, and a kickass soundtrack. If you like your cop shows messy, and your serial killers messier, you're going to love this.