This is one of those cases, a bit like Jaws, where the media adaptation is clearly better than the book. Don't get me wrong, the book does have a very clever voice for Dexter, so it's very easy to see why someone thought it would make a good TV series, but the show... in addition to the standard perks of having actual humans performing the parts, cinematography, and other such advantages movies have on books (sorry, books, it's true. But hey, at least books can't have Paris Hilton star in them), the TV series has more time to unpack the plot, which DDD rushes through at a somewhat unbelievable pace. There's a lot of cases of Dexter "just knowing" things, while in the series, this is the result of an ongoing dialogue between Dexter and the Ice Truck Killer.
( Compare and contrast and spoilers. )
( Compare and contrast and spoilers. )