Your description of the dark atmosphere made me give this show a chance, and boy does this show have a dark foreboding mood to it, it quickly drew me in, and now I am almost finished with the first season already.
There is consistent theme about how people behave when stripped of compassion through abuse, the changing and instability society, or by ideology. I find it morbidly fascinating. If you look the show up on Imdb you will see a lot of critiques complain about the shocking and frequent violence. For me, though, it helps reinforce a feeling of a dark human nature coming out in a society and is increasingly desperate to hold together.
I would rate it like a 8.6 / 10, and for reference a show like Boardwalk Empireould be just slightly higher at 8.8 for slightly better acting, and Steve Buscemi.
My only possible complaint would be missing out of bits of the dialog at times due to all the Brit style speakin'
