Go back and watch the Packers Week 1 win over the Chicago Bears last season. It was probably the best game the defense played all season with the possible exception of Week 16 against the Vikings. There was one player who was a big part of what the defense did in that game who was missing for the rest of the season: safety Raven Greene.
Greene went down with a season-ending injury in the third quarter of the Packers Week 2 win over the Vikings. The defense certainly felt his absence both when defending the pass and trying to stop the run.