My biggest complaint here is how the movie is shot. Kung-fu films are special in the cinematic world because they are given immense leeway in every part of the moviemaking process as long as they show us some incredible fight sequences. Sure enough, RZA filled the flick with fights, blood and gore, but he used the more American style of filming, which involves many more close-ups, quick cuts and intentionally shaky hand-held camerawork. It ends up making the fights less impressive because the audience can hardly tell what cool manuever the person is pulling off, it's just a close-up of limbs and legs flying around. Paul Greengrass failed the same way when he made The Bourne Supremacy (but then regained his senses in the next chapter, The Bourne Ultimatum). The fights are the most important element of these movies, so showing them cleanly and clearly should always be of the utmost importance.
Right beyond that gripe would be RZA himself. Again, I give him great credit for getting the whole project together and pulling in some really great actors (Lucy Liu, Russell Crowe, and legends of the genre like Corey Yuen and Gordon Liu), but casting himself in the lead role proved to be the wrong move. There is definitely a precedence for leads in these films to be stoic, pure-hearted men dragged unwillingly into the fight, usually hiding their intense emotions at bay for fear of the violence they could unleash, but RZA lacked any emotional intensity on-screen from the first moment almost until the screen went dark. At times it looked like he just didn't even want to be there. A switch in the starring role might have given this fight flick some legs to stand on, but I can't go as far to say it would have suddenly become a good film.
Honest effort, but missed the mark.