My pet peeve with this team has been its absolute, utter inability to get off the field on third down defensively. That's been the story since '03. They cannot get off the field on big downs. If they can do that (i.e. get some heat on the quarterback and stuff a run once this century), it will go a long way.
Seriously, if there's a stat for third-down efficiency for opposing teams against the Bills defense, I'm willing to bet the Bills rank in the bottom five in the league.