Brillant piece of work from Scorsese. Well written and acted. Nicholson was outstanding. I only watched this recently prior to that had only seen segments. I was gripped by the battle between
the two main leads as the plot began to unravel a great piece of cinema. Hats off to Scorsese for producing once again a master piece.

I've seen it two times already and i want to see it again,very good film.You have Jack Nickolson,Leonardo Di caprio,Matt Damon,Mark wahlberg and many more stars in this movie and above of all that Martin Scorseze directs,no doubt this one is a masterpiece!!!

and make sure you also try the original asian version infernal affairs I (as part of a trilogy). i saw this asian version first: a really good good cop/bad cop movie, very convincing.
the american remake is also very good but if you know the original story, it stays a remake. nothing to be ashamed of because with this very strong cast and a class director qualitiy is assured. good entertainment. telling you about the plot would spoil it.