Darker than Black has a large cast and an intricate world. It probably takes more than a single episode for the characters' motivations and stakes to become clear and for the show to hit its stride, but if you don't mind a bit of a jumble, the first episode of Darker than Black is pretty good. There's a lot here, enough that it's hard to keep track of it all—but the premise makes some interesting promises, and I'm left wanting to know more about the various factions at play and their goals. It would be hard to distill, from this one episode, what the overarching plot will be, but we can guess that it'll involve spies, detectives, hit men, and various other unsavory sorts running around with superpowers in a quasi-apocalyptic Tokyo.
The art is distinctive without being jarring, and the production is pretty good throughout. The most main-character-like character is both lovely and alarming, and there seems to be a sidekick cat, so color me sold. The ensemble cast of not-high-school-students is also a strong selling point.
Recommend: Yes.
Rewatch Disclaimer: I've seen Darker than Black and it's largely excellent. For some reason it was very hard to separate my rewatch impressions from my knowledge of the show; the first episode contains a lot of mystery and I kept catching myself filling in the blanks, or being like, "oh yeah, this is so-and-so who will go on to do such-and-such..." So my bad, but ultimately what you're looking for is a recommendation, and this title holds up. There's a slight drop in the climax of the series, and the sequel (Meteor Twins) is a huge let-down, but this isn't a show I would miss.