It felt like a sequel ...
there was so much back-story in the movie I felt I had missed part 1 and was watching part 2.
Part 1 would have had a good story-line, as outlined by the mayor - criminals running riot post 9/11, a special team of cops being formed, taking down the bad guys, but in the process the cops becoming corrupt and Statham exposing them, leading to his own downfall, but saved by the love of his wife.
That, as part 1, would have made this film and its characters a lot more complete with the only new main character being introduced in part 2, the young Chinese girl.