Van Damme tried to do it in Timecop. Schwarzenegger tried it in The Last Action Hero. It seems every action hero has to eventually face himself. Literally, by playing his twin. Jet Li decided to get a head start by doing this movie relatively early in his career.
I really didn't expect much of this movie. The plot is complex: 125 parallel dimensions exist. A member of the Multiverse Bureau of Investigation accidentally kills one of his alteregos in a parallel universe and discovers that he becomes stronger, faster, and more powerful. Realizing that, if he kills all of his multiple selves, this process can make him a god, he goes off on a killing spree in the most egregious example of self-loathing this side of sci-fidom.
WAY too many critics put this movie down for its special effects. Specifically, that the effects mimic the Matrix. So what? Seeing Jet grab two motorcycles, one in each hand, and smash a man to death with them is a thrill. He kicks cops out of thin air, dodges bullets, and jumps across buildings. That's the best part of the movie.
The problem is, Jet Li just can't act. Or I should say, he can't act well. The plot demands a lot of him -- this is a rare instance of a script being better than the actor can handle. Jet Li is supposed to weep over his wife's loss, act in multiple roles as his multiple selves, display rage, hope, madness...more than most people display in a year. Jet can't do it. His English is quite good, but he simply doesn't have the range.
And in a movie all ABOUT range, Jet can't pull it off. But that's okay, what he does is some amazing martial arts, demonstrates really cool special effects, and provides a funky plotline that inspired me enough to want to run a mini-campaign in this setting (maybe I will, hmmm). That's the highest compliment I can give any movie.