Oldman’s taciturn performance (he doesn’t speak for the first 20 minutes at least) reminds us that the less an actor “does” the more profound the performance appears because it lets the audience do the work of reading depth into the character (cf. Drive). That isn’t a knock on quiet performances, because not all actors have faces interesting enough or eyes expressive enough to sustain such sustained study like Oldman (and Gosling).
In the central scene Smiley (Oldman) recounts an encounter with another spy which feels a little too actorly only until one recognises that in any other film this scene would have consisted of a flashback — indeed, this film itself employs flashbacks many other times — and the significance of the episode is what it means to Smiley now. Indeed, it implicitly explains his modis operandi and why he is so reluctant to reveal himself through speech.
It is a very good movie whose total absence of genre competition might make it look great by (lack of) comparison. Its most evident accomplishment is recreating the dreary atmosphere of a 1970s cold war thriller — though “thriller” doesn’t seem appropriate given its pessimistic view (despite a Wire-esque concluding music montage) of counter-espionage policies as inherently destructive of trust and relationships. If American cinema in the 70s was charactertized by the Active Paranoia thriller, then this British film by a Swedish director is a portrayal of Passive Paranoia — the life-sapping fatigue effected by suspicion as a professional state of mind.