Just saw this last night and it is a masterpiece.
I haven't seen the acclaimed BBC mini-series and except for his small part in The Spy Who Came In From The Cold I haven't seen (or read) any George Smiley yarns.
So I went in fairly cold.
It's impossible to discuss given the extremely convoluted plot machinations, but the acting was superb. It should definitely win the SAG best ensemble award (although I suspect The Help or The Descendants will take that prize).
Oldman is as good as you've heard, as are the respective actors who play the titular Tinker, Tailor, Soldier, and Spy.
And watch out for Benedict Cumberbatch who just about steals the movie with a nail-biter of a sequence.
Cerebral and completely unglamorous, this is espionage as mundane workaday business.
Easily in my top 5 for the year.
....but the world goes 'round