The annoying voice was bad enough, but the fact that he NEVER shut up at any point in the movie made this thing unwatchable. As they flee in the streets and hide from people trying to kill them, they still have time to sit and babble endlessly, and always loud enough to ensure that anyone looking could find them. Without ruining the movie for anyone who wants to witness this trash for themselves, I will say that the bus scene is the most absurd and annoying of them all.
Mos Def ruined the movie all on his own, but Willis didn't really do anything stop him. He could play this part the way he did in his sleep, and it looks like he did. The man playing the archetypal "bad cop" was just as lazy adding nothing to the hackneyed script and even contributing to its unoriginality with clichés of his own. This character's mindlessness, particularly in his final scene, was idiotic to the point of insult.
To be fair, the plot was interesting enough. If it were a little less cliché and unrealistic, and much better done, this movie would be as good as any run of the mill action thriller-type. I did find myself trying to add complexity and originality to the story as it went, though. As it is, it has to be one of the biggest wastes of time and $7.00 available to the general public.