Devin McCourty: A+
McCourty didn't play in the season finale, but the Patriots will certainly welcome him back on the field for their playoff run.
He was a rock in the secondary, so much so that quarterbacks rarely threw in his direction. According to Pro Football Focus (subscription required), he was targeted only 27 times on 610 plays in coverage.
Aqib Talib: A+
Talib was the best player on the Patriots defense when healthy. He shut down his assignment almost every week—Josh Gordon and Steve Smith were able to gain some yards on Talib—and was a solid open-field tackler when necessary.
Talib will certainly be a priority for the Patriots in the offseason. He has earned himself a lucrative contract.
Logan Ryan: A+
Ryan met and exceeded every expectation that you could think of as a rookie in Bill Belichick's defense.
He ended the season with five interceptions and will certainly get plenty of chances—whether Talib is re-signed or not—to add to that figure next year.
Kyle Arrington: B+
Arrington was beat deep on a few plays, but he had another positive season for New England. He also recorded a pair of sacks and was solid in coverage when not asked to be the No. 1 or 2 cornerback.
He won't be a star, but you could do a lot worse for a nickel cornerback.
Alfonzo Dennard: B
Considering that it wasn't a sure thing that Dennard would play this season due to legal issues, any contribution he made is a bonus.
When operating at 100 percent, though, Dennard was equal to Talib. Unfortunately, Dennard's lower extremities betrayed him on multiple occasions in 2013.
If Dennard is able to work on his tackling, there is no reason that he can't be a top corner in the league.
Steve Gregory: C+
Gregory was a big part of the defensive success early in the year, but it seems like he has been slowed by injuries to his thumb and knee.
His tackling got worse as the year wore on, and lapses in coverage occurred more often. I wouldn't be surprised to see rookie Duron Harmon as the starter next season.