The fact that the soundtrack goes all Eastern (Near / Middle as opposed to Far) whenever there's an Islamist slant to the storyline.
Its a lazy broadbrush stereotype - perhaps a cinematic attempt to fathom the zen-like thought trance within the hypnotised mind of the suicide bomber, but both wrong and unneccesary. And it brings to my mind the kebab shop down the road (another broadbrush stereotype, I know, but I'm not a spy drama.)
Aside from that, brilliant soundtrack.
The non-appliance of science. Each time the techonology envelope is pushed slightly further outward, from that moment onwards I end up wondering why they don't use this incredible gadget or that handy algorhythm in future episodes.
Last series it was some amazing sort of bug that could be secreted just about anywhere that really got my goat (Gary) more than it deserved. Last night it was two things - a gamma aminobutyric acid derivative which knocks out your prey and makes them hypersuggestive when they awaken, and the two-way transmitter injected and attached to the bones of one's skull, making it invisible and utterly soundless in output.
The spectre of James Bond and his Invisible Car rises...
The sheer fact that it doesn't have Henry from Neighbours, Marcus Tandy, Jan from Howards Way, the wife of Marty Hopkirk (deceased), or Ros from Bugs in it.