Producers Daniel Cerone and David S. Goyer did some press recently for NBC's "Constantine," their upcoming series adaptation of DC Comics' supernatural title "Hellblazer" starring Matt Ryan as John Constantine. They told io9 that their main aim was to go "straight back to the source material". Goyer says they're not adapting any one specific storyline, but they will "be sort of weaving in and out of them" and suggests they might even for a version of the Dangerous Habits storyline down the line (around season three or four should it get that far).
The first season though will be heavily inspired by Constantine first appearance in "Swamp Thing". Cerone says: "That's when we're meeting him in our series. In fact, the American Gothic storyline heavily inspires our first season arc, so all the things that happen to Constantine over the course of the thirty-year run in the comics, it's all ahead of him."
Asked about using other DC characters, Goyer says: "We've been given sort of permission from DC Comics, Geoff Johns and the rest of them, to use the other people from the occult DC universe, so as long as they're not in spandex, we can kind of use them." The plan is to include a few in the first season in hopefully recurring capacities.
Finally they were asked about the show's content and how dark they intend to go. Cerone says: "I was a showrunner the first two seasons of Dexter and our development executive at NBC and the president of Showtime at the time, Bob Greenblatt, they were the two supervising executives on Dexter. That's their sensibility. They want to bring that kind of programming, that kind of edge and that kind of darkness, that kind of moral ambiguity, they want to bring that to network television and they're pushing hard for it.