Not bad, really. Since it's only 12 episodes long, it's worth a shot.
The animation is great. The world building is good too. The characters are interesting enough, not very cliche or typical. The dialogues are average, but not unpleasant. The pacing is good. There is very little fanservice, but it's heavy on violence and mature concepts like killing, manipulation and death.
[SPOILERS AHEAD]
The female protagonist, Sawa, is strong and very goal-oriented. One thing i noticed is that she's very emotional. It's not really a problem, but all that screaming is a little annoying. All throughout the anime, it is said that she's exceptionally powerful, but the fight scenes don't blow your mind like some of the typical shonen anime. Moat of the time, she's either screaming at the villian or crying out in pain.
Her adopted sister, Asahi, like most anime children, is a bit annoying but a major driving factor. I should have seen her death coming to be honest, but it was still a little shocking, and I have to admit, a little sad too. When she comes back a few episodes later, I was a bit annoyed as it felt too cliche and meaningless, but hearing that it was Sawa's blood that brought her back to life and then showing that thus, Asahi is now the last remaining link to the Karasumori Clan made sense and then it didn't seem unnecessary anymore.
The other characters, Hana and Tsuki are unique in their own ways. Hana is your typical seductress but her friendship with Sawa was really interesting. I was a little miffed at how much she changes with pregnancy as it felt like the author was disapproving her old life and encouraging motherhood and marital life but whatever, Hana would make a great mother I suppose.
Tsuki had way too many changes to really make sense of his character. The ever changing alliances made him untrustworthy. I think his main agenda was his obsession with Sawa, which by default made him annoying. There was a point where I found myself pitying him but that disappeared when he came looking for Sawa and Asahi and all the events that happened thereafter.
Jin is a well-constructed character. I was a bit skeptical at first, given his loyalty to the government, which appeared to be dystopian and ultimately harmful to society. But he was obviously worried for Sawa. As the anime progresses, i began warming up to him. The twist at the end was totally unexpected but at this point, I was too confused to hate him. In the end, he defeats the main antagonist. I felt like he was taking the moment away from Sawa but understand that it's necessary to ensure that she doesn't go back to her old life and it's his way of protecting her from a life of blood and violence which he knows is his fault.
The end where the villian is revealed seems anti climatic and disappointing. We can almost feel Jin's disappointment at being controlled all his life by a mere symbol. But he does what he's supposed to do and that's that.
There are a lot of deaths in the anime, and a lot of 'yeah, no they are not really dead' moments too. The plot twists are good and unexpected. On a whole, it gets a little rocky in the second half but concludes very beautifully and very meaningfully.
It's not bad, really. You can give it a shot and easily finish it off within a day or two.