This is not an action-packed spy thriller, so modern readers unfamiliar with a John le Carré may be frustrated by the slow pace and wordy heavy narrative, but it worked really well for me. There are elements of the writing that create such a vivid image in your mind that it's like a film running in front of you (a descriptor of a pretentious moped springs to mind). This is a dull, drab world with spy craft that is about details rather than action and essentially nothing happens and despite that it's compelling reading and the rich tones of the narrator for the audiobook enhanced it all further.
This is book 3 in the Karla Trilogy so there is history which does enrich the story but reading out of order can be done despite that.