I didn't bother finishing this. I lasted ten episodes, got bored and gave up. It's dreary, it's charmless and I didn't care. It's a grim near-future story in which everyone seems to be either a victim or a professional killer and the showrunners' heads might have exploded had anyone in the show laughed or even smiled.
Actually, no. That's a lie. The temporary protagonists of eps.7-8 are entertaining and they briefly make the show lighter, but still not particularly interesting.
The premise: a Big Alien Something appeared in Tokyo ten years ago, changed the sky and gave some people superpowers. These people are called Contractors, but their powers came at the cost of their humanity. It's believed that they've lost all their loyalties, emotions and conscience. They have no problem with killing. The name "Contractors" comes from the contracts that mean they have to do something specific after using their powers. This might be as simple as just eating food or smoking a cigarette, but it might also involve breaking one of your own fingers.
There are also Dolls, who are even less human.
Theoretically, there are some interesting stories. I quite liked ep.9, with old school friends on opposite sides of the law. I didn't care about those characters either, but at least I was no longer comatose. There's a name-changed version of James Bond and MI6. I quite liked the girl in ep.2. Nonetheless, anything of interest that might pop up was always in danger of being drowned by the show's inherent dullness.
Personally, for me, the oddest thing here was the theme music, because it's from a Japanese band called "abingdon boys school". They took their name from Abingdon Boys' School... which I attended. For seven years. (I don't remember anyone ever calling the school by that name, incidentally. We just said "Abingdon School", even though the town has other schools, or perhaps "Roysse's".)
Verdict on this show: absolutely not. It's not bad as such. It's certainly not "so bad it's good", or anything like that. That would have been better. Instead, the show's bloody-mindedly and humourlessly crushing anything I'd call entertainment. What's more, I've read that the second season is generally regarded as a step down in quality from the first. The only fun I've ever got from this po-faced series is a fan-made anime music video called Darker than Duck, which amused me by playing clips from it over the theme music of Disney's Darkwing Duck.
Even someone desperately looking for anime shouldn't watch this.