The Patriots defensive line did what it is supposed to do in a 3-4 alignment: not get noticed that much. They absorbed blocks well (particularly Vince Wilfork in the middle), created gaps, and allowed the linebackers an opportunity to make plays.
The Patriots defense allowed the 4th fewest points in the NFL (17.1 per game), sacked the opposing QB 47 times (2nd in the NFL behind the Giants), had the 6th best pass defense in terms of yards per game (190.1), and the 10th best rush defense in terms of yards per game (98.3).
However, those defensive stats are skewed. The Patriots offense was so good and put up so many points early in games; that opposing offenses were forced to pass the ball. This allowed the Pats' defense to tee off on the quarterback, and play a pass-oriented defense.
The Patriots allowed 4.4 yards per carry on the ground, which was 26th in the NFL. That number is atrociously poor. And in close games, the opposing teams took advantage of this below average run stopping to drain the clock and get first downs on the ground.
The quality of a defense starts and stops with the defensive line. The Patriots' defensive line will look very much the same in 2008 as it did in 2007. Seymour and Warren on the ends, Wilfork in the middle, Jarvis Green coming in on the outside, and Mike wright (who recently signed a new deal with the Pats) backing up in the tackle position.
The Patriots lack a quick upfield rusher on the outside of the line. Seymour and Warren - both tackles in college - are good at holding up the offensive linemen, but neither possesses the speed to go upfield like a Dwight Freeney. Then again, very few linemen in the NFL posses that kind of speed.
I'd like to see more 4-3 played by the Patriots, especially with an ancient tedy Bruschi in the MLB spot. Jarvis Green was 2nd on the team in sacks with 6.5. Warren had 4, Wilfork had 2, and seymour only had 1.5 (although he missed considerable time with an injury). A front four of Green, Seymour, Wilfork, and Warren would be menacing. Green could rush hard off the end, and Wilfork could use his strength to plow through up the middle.
Adalius Thomas will probably see most of his time at OLB in 2008, and he too can come up and play defensive end. He tied for 2nd on the team with 6.5 sacks, and a full season on the outside should see that number increase. Mike vrabel can also play end should the need arise.
Overall, the defense performed solidly, but they didn't make the massive game-changing plays we've seen from them in years past. Seymour was mediocre in the games he played, which was a big part of this.
The likelihood of a suceptible defensive secondary is very high in 2008. But holes like that can be hidden with a powerful pass rush driven by the defensive line. The Patriots must figure out someway to get more pressure from the line in order to be succesful in 2008.