I'm surprised it took me this long to watch the first season of Darker than BLACK, but the second season (Gemini of the Meteor) started this Fall 2009... usually when something really good gets a second season, my anime friends like to chat up a storm about the first season and this means spoilers galore! It took me little over a month to watch all 25 episodes and the 1 ova episode, but this is because I tend to watch 15+ anime at the same time (more recently more because I've been watching some old anime I never saw such as Speed Grapher).
Darker than BLACK is an original anime (meaning it is not based on an anime, manga, game, etc but is an original creation by the company that made it) produced by studio BONES. It has two manga adaptations. Season 1 (Kuro no Keiyakusha) ran for 25 episodes and had one ova (it's known as episode 26, but takes place in between episodes so is not actually the end of the series but more of an extra episode). The second season premiered during the Fall 2009 season of anime and has 1 ova episode planned, but this ova is set to tell more so Hei's story from before season 1 started. FUNimation entertainment has the license for an English dub and season 1 has already been released completed in English.
In Tokyo, an impenetrable field known as "Hell's Gate" appeared ten years ago. At the same time, psychics who wield paranormal powers at the cost of their conscience also emerged. Hei is one of the most powerful of these psychic agents, and along with his blind associate, Yin, works for one of the many rival agencies vying to unlock the mysteries of Hell's Gate. [ann]
I was expecting this anime to let me down mainly because when people overly fan boy/girl over a series, it ends up being extremely cliched or something I've just got no interest in seeing (there are a few cases where a really popular anime was one I liked). I found it to be brilliant to add a payment for these 'powers' used in the anime, which without would have made this over used "we haz powahs!" concept even more over used and I probably would have been bored within a few episodes, but add the amazing character relations and this mysterious grim reaper type character BA BOOM you got a winning series :]