I attempted to view this drama series sometime back and didn't progress very far. It isn't poorly made, though its deliberate pacing proved off-putting for me—typically I don’t mind that kind of thing, but spy narratives aren’t really my cup of tea. I decided to revisit it not long ago, and managed to finish watching it this time around without issue. There are moments of action and a bit of dramatic flair, but largely the show consists of dialogue and an understated sense of suspense throughout. I will admit that there were instances where I was unclear about who was involved in what behind the scenes, yet I never completely lost track of what was happening. Alec Guinness delivers a strong performance. He portrays a character who suppresses his feelings to carry out his duties with objectivity and focus. A few of the side stories, like the retired spy’s role at a prep school, initially seemed superfluous, though in that particular instance, it ultimately proves worthwhile. I don't foresee myself rewatching this series anytime soon, but I would suggest it to those who appreciate spy tales without excessive action or brutality, particularly if they are familiar with John le Carré’s work.

Source on TMDB