I did not expect the novel to be so similar. John le Carre's style is very much understated and there are passages that remind me more of Charles Dickens than Ian Flemming. If you've just read a Dan Brown, you'll likely find it frustratingly slow and uneventful. That doesn't mean that Tinker Tailor compares unfavorably to today's fiction, quite the contrary. It doesn't try to wrap everything up in a sentimental finale, where the heroes prevail and love triumphs. Those tricks are reserved for Ken Follett and the likes.
But I have to say that I still enjoyed the film more. Not because the novel is inferior, but because the actors are wonderful and the script is just the right combination of not saying enough and implying too much. In a way, it is almost a breakout feature for many of the cast involved. Benedict Cumberbatch was on the up and up but not yet successful, Tom Hardy was perfectly cast as Ricki Tarr. Even the eponymous Tinkers and Tailors were cast so well that even though they remain background characters, you can feel the back story there. A big thank you to le Carre for writing it and Tomas Alfredson for directing it.