At a certain point, long after my brain stopped caring, I suddenly remembered this feature was directed by Ryûhei Kitamura. It was then I understood what the problem was. Kitamura drops a metric ton of style upon a rather simplistic story. This makes the characters, story, and um... everything as stone cold as the film's steely blue cast and as heavy-handed as the swing of Vinnie Jones' steel mallet.
Might as well just end it there. There's honestly nothing else to go. The scope of the meat train's influence is easily pegged if you pay attention to jewelry and the protagonist's ultimate fate isn't that hard to guess. The reason for all the unfun killing is a mild surprise, but besides that everything is on the screen with no ambiguity to exercise your mind. It's gory in a CG kind of way, but man this is one bleak underground train ride to absolutely nowhere. All the studio bullshit surrounding this one turned out to be no big deal.