Schematic but tense and quite sad story of alienation involving a cop who goes undercover in the mob and the gang mole who infiltrates the police. Strong performances by Tony Leung and Andy Lau as the two men living a decade out in the cold. One of the better gangster film of the century.
I can't really decide what was wrong with this film, it was quite well done but after falling asleep twice in it I would just class it as uninspiring.
What is good about it however is the soundtrack (although the music is a little odd), there is an uncompressed PCM 5.1 option which is stunning and ranks amongst the best I've heard.
Turn it on and listen loud, it may keep you awake!
It certainly had it's moments which is why I would probably give it an 8/10 (4/5 on here) it's interesting how it came to influence The Departed so much but in it's own being a good movie and having many memorable moments, the performances like Steve said are great and one of the reasons why this film is so good.