The second series slows down even more dramatically, and becomes so dark it is black of the blackest kind. Still good, but not as strong as the first series. This is so slow it has to be binge watched (I think) in medium doses, maybe 3 - 4 episodes at a time. This would not work if it was released and watched weekly, too many would lose interest and flow. The flow when watched around 4 episodes at a time makes it more easy to find the flow amongst the slow, but the drag in pace does become a little monotonous.
Cast are well chosen for the main part, some characters develop a lot more slowly over time, but are done with some intelligence by the director and producers. There is sometimes a little too much emphasis on side-ways glances and surreptitious looks and reactions, done sometimes to distract, sometimes to raise suspicion, sometimes to direct our attention (all normal), but does sometimes lack a little subtlety in the directorial execution. My assumption this is done for the sake of an international audience.
Plot is engaging, has enough intrigue to build interest, contains a complexity that is allowed to unfold over time that requires a little patience (which gets rewarded), maintains a pace that doesn't quite keep you on the edge of the seat, but nor does it set out or pretend to try and be people swinging from exploding buildings or planes at 20,000 feet.
Finally, a comment to the few reviewers claiming "anti-american" script, I would recommend watching more than the first opening scenes. This is a story, entertainment, all based around espionage and intrigue. Chinese are keeping secrets, Aussies are keeping secrets, the Yanks are keeping secrets, heck - everyone is keeping secrets from everyone. The plot revolves around exploring 4 concepts - Money, Ideology, Coercion and Ego. It's not even CLOSE to being anti-American, but it also does not paint America as the untainted hero to the world. Surprise surprise, NSA, CIA etc have done some questionable things at different times in history. Whoopdy frikkin' doo. Welcome to Earth.
Having said that, I found the movie beautiful in the detail. This is not about grandiose plot, high speed chases and super cool cunning people. This is accidental and bumbling happenstance where random events are delightfully used. Truck, garage door etc. I carried with me the finer and more easily lost details of each character and I found they surprised me and delighted me with often times whimsical twists and subtle growth/support. I didn't find any huge character surprises or character twists, just good solid development, the kind where you can leave your opinions open to the end. Times like the late night rendezvous at the juke box joint and what happens when Bob tries to dance. Perfect. I walked out with a smile on my face, well amused and very much liking the attention to detail in character, shots, lighting, soundtrack etc. Not edge of the seat, sit back and relax.