Opinions now it's finished? SPOILERS
Let's start with the negatives.
- The writing / plotting could have been much better... For an episode and a half, they're merrily doing their detective stuff. Then, Susan meets Cavendish and he tells them exactly who they're looking for.
- There were a couple too many characters going: "I signed the Official Secrets Act, don't you know? But, with relatively little persuasion, I'll happily tell you everything you need to know."
- There wasn't really any "jeopardy" towards the end of the last episode, as the other three knew exactly where Susan was.
- How exactly they were using their Bletchley skills to track down the killer could have been explained a little better... Having read a biography of Alan Turing, I know that detailed explanations of the processes used at Bletchley can very quickly start to go over the head of someone who doesn't have that sort of brain. But, on several occasions, it wasn't really clear how the four had come to a particular conclusion.
- While obviously done on the cheap, the period detail was generally OK. But, I did get a bit fed up of seeing the spotless exterior of St Pancras station - it would presumably have been very grimy in the '50s - and the very un-1950s ironwork that was put up outside during the recent refurbishment.
On the positive side...
- It's very rare for anything on ITV to even tempt me to watch, let alone hold my attention for a whole series - by ITV standards, this was about as good as it gets.
- The basic idea was interesting and intriguing.
- The acting was very good.
- Despite its faults, I really rather enjoyed it.
I would be interested to see another case involving the four. Though, I would want the writing / plotting to be rather better and a little more effort put into the period exteriors - no more St Pancras station and its anachronistically gleaming exterior, please!