too short *Spoilers*
I saw The Departed first, so maybe that's why it felt shorter. I don't think it's a bad movie, but it moved too fast. I would've liked to see Leung beating people and misbehaving more as a cop and see more of the chief. If you saw more of the chief, you would feel even more sad when he gets thrown off the roof (even though I felt more sad about ti in IA than in Departed). Leungs character misbehaving would make the psychological theme of this film (which I think is just genious), which is that the two maincharacters don't know themseles if they are good or bad.
Still liked this a bit more than the Departed. The Departed just told a story, when Infernal Affairs had a psychological theme. Just wish it wouldn't rush through. It felt like the movie just begun after Sam got shot.