This is not an easy watch but I feel many reviewers have been too hard on it. Many of the actors (especially Lena Headey) and special guests have put in strong performances. I cannot comment on suggestions of scientific accuracy that many have brought up but I don't think that is really the point and I am sure most sci-fi can be accused of that to some degree. It is a complex plot with a timeline that is not immediately intuitive to follow. You will not be able to watch this while chatting with friends as you won't follow what is going, it will require your full concentration. The question is whether all that hard work is worth it? For my part, I largely enjoyed it and it certainly gets better from about the third episode but I wouldn't watch it a second time! Why the makers made it so difficult to follow in such a non-addictive fashion is beyond me. I presume it was a style thing - taken a bit too far IMHO. There are some interesting ethical questions asked for this day and age and the story, once unravelled, isn't bad. Production is also pretty good. In short, don't sit down and expect a nice easy plot like you might get in Star Trek!
