I didn't know anything about this book before I started reading it, so I had no assumptions about what would happen. le Carre writes masterfully, and I enjoyed his prose and execution of plot. The problem with a lot of espionage and detective novels is that the author typically focuses on all the action and dialogue and leads little in the way of description, and you rush from car chase to gun shootout, and then get a final wrap-up at the end of everything. Tinker Tailor isn't one of those. It reads like an espionage novel for the intelligent reader. It slowly builds, putting the pieces together one by one.
Each character had a distinct personality, going beyond the standard physical descriptions, but truly giving life to each one. I think this portrays a rare author. I was amazed that I was actually able to keep track of every person mentioned!
What got me was the slowness of the novel. I haven't seen the movie, so I don't know how it is portrayed, but much of the action described is re-told through dialogue as Smiley investigates among other agents. I kept waiting for a big action scene. And the end was a disappointment in this regard. However, I think that because it wasn't that type of novel, it was more genuine. Tinker Tailor isn't supposed to be that way.
Now that I think about it, I wouldn't mind reading it again, to see what I missed the first time around.