I found it absolutely riveting if a little difficult to follow at times. It's certainly a convoluted plot and best seen in 2/3 sittings unless you've got a really good memory.
Can't agree with some other reviewers who've given it a pants rating. It's one of the best shows I've seen in years. I'll see it again in a few years time as it was so good.
I'm getting straight on with Series 2 now.