The Scorsese movie would be The Departed, right? I might give it a watch, just to see how it compares. Wikipedia says the script for Infernal Affairs was inspired by Face/Off, by John Woo. It’s funny how that goes, American film inspires HK film which inspires another American film.

The double infiltration scenario was really cool indeed! One-dimensional bad-guys can be rather predictable and boring, it really is great when the antagonist has some good-guy traits. :D