Put in effort and you'll get the reward

Rating: 10/10 (10 September 2017)

First off, unless you're prepared to this multiple times you'll not get the shear brilliance of the film.
Every second counts in this film. There is no filler whatsoever. Watch it once and it's good (maybe not fantastic), after the 20th time of watching it becomes apparent that this is one of the best films ever made.
The film moves along with a pacey melancholic jazz score which meshes with action. Action in this case is doors opening, lifts whirring and railway points changing and which in this film are infinitely more powerful than exploding buildings, shootings and car chases. The film captures 70s London: grimy buildings, dull light, offices sinking in paperwork, clanking analogue machines, bland food and uniform like clothes.
Everyone has a secret weakness which they hide with varying degrees of success. The film shows this in the expressions of the actors more than dialogue. Every actor in this film plays a blinder. Clearly Gary Oldman is up there. His Smiley is expressionless most of the time and dialogue delivered in studied way, however, he only has to modify this slightly to make it count, when he does the effect is devastating. The other actors deserve credit: Toby Jones constantly peevish smug Alleline, the haunted look of Mark Strong's Prideaux, Colin Firth's self satisfied Haydon and David Dencik's anxious ingratiating Esterhaze. There is a classic 'wtf have I done' moment of acting from a bit player that is fantastic, if you've seen it you'll know what I mean.
The last 10 minutes wraps up the film completely and the inspired choice of soundtrack counterpoints the repressed desires of the key leads.
Finally the plot is straightforward and linear, but it is made up of many many links which slot together seamlessly. At first watch you may miss many of these. On each re-watch another link will emerge which will further tie things together so making it a better film each time.