Gary Oldman is indelible as George Smiley. Men who are almost elderly are often a little vulnerable. They may be facing a loss of professional identity and social relevance without having yet reached the mitigating dignity of old age. At the beginning of the movie Smiley--slowly breaststroking through a pond, being fitted for new spectacles--seems considerably more diminished than he subsequently turns out to be. "He's a fanatic, so we can stop him, because a fanatic is always concealing a secret doubt," Smiley says. Pow.
The movie is beautifully crafted. I'm not sure it works as a spy thriller. As a lot of critics have commented, the plot is byzantine, but beyond that, there's an implicit critique of both spying and thrilling. Are you supposed to be rooting for British intelligence, or for Smiley and his skeleton crew of allies, who are in some sense working against British intelligence agents, who are--setting aside the fact that they have a mole--dysfunctional, duplicitous, and corrupt? As a drama about spies, though, it's terrific.