For a long time Antoine Winfield was the most underrated D-back in the league. Griffin is not quite that good, but he is the most underrated player on the Vikes defence. That is why the Vikes gave him a new contract.
He struggled at the beginning of the season against the Bears in that heartbreaking 48-41 loss. Later in the season against the Bears he helped force three picks by Kyle Orton.
He is essential to the Vikings run defence. People look at his tackle total and think that QB's like to pick on him, but at least half of that tackle total has come at the line of scrimmage.
He, in my opinion, is a very reliable starter and can only get better, especially with Antoine Winfield as his role model. Will he ever be a pro-bowler? I think he has that potential, but look at Winfield and it almost didn't happen for him.
Next year when QB's try to pick on Griffin, they will be in for some nasty surprises.