Deserves its place in the top sequels list, I love how different it is from the first.

Infernal Affairs 2, the prequel to the film that inspired The Departed. The focus is more on the fall of Inspector Wong and the rise of Sam in the underworld than on the undercover moles, but since those two were one of the best things in Infernal Affairs, I'm not complaining. A little confusing to get into, but the end gambits are so great, you just have to cheer. Except it's a tragedy. And great main villain in Francis Ng too (oh and Carina Lau is a luscious leading lady).