Ok, I'm probably the only retard who forgot Infernal Affairs 1-3 was the basis for the Departed. That aside, this movie was fantastic. I've seen Departed - enjoyed it. But Andy Lau and Tony Leung Chiu-Wai have acting chops galore. Actually, the entire cast is 100% believable. It's an amazing crime drama exploring moral shades of gray in the context of undercover police work. Michael Mann's Miami Vice did that very effectively, also. But Infernal Affairs is the best undercover drama I recall seeing on DVD -- ever. (I will admit that I'm still a sucker for the undercover action flicks like Bad Boys).
If you haven't had the priviledge of picking up this DVD, don't watch the trailer yet!!! I haven't seen parts 2 & 3 (which I assume won't be as good as 1), but I can't pass up buying the 3-pack DVD box from Amazon for $30.