I really enjoyed it and thought it looked stunning, I can't think of a film which captures a time more brilliantly or is as evocative of the period (unless it was shot then!).
But the sets are almost so good that I found myself distracted and staring at lamps and missing bits of dialogue. My other reservation is how real the characters are - other than Smiley who is amazingly done by G Oldman reining it all in, much respect to him.