They will get better this year but will never be great. So be prepared for them to give up a boatload of yards and a far amount of points. If your league awards or penalizes for those two items, there are better options.
At some point I believe they will start to get some sacks and should get some turnovers. They were worth a lot last year because they forced a ton of turnovers and then got a bunch of return TDs. THose to me are more fluke plays than anything else and very hard to predict (and repeat or rely on).
Three things to consider:
The current defensive unit has had very little time to play together so like Ocho on offense need to get used to the system and their teammates.
The defense has several guys banged up or hurt. If they heal up and all get on the field, that wouldn't hurt their cause.
NE teams and defenses generally get better and improve as the year goes on. This year, maybe they go from bottom 10 to middle of the road. They probably won't get a ton of sacks, so people are banking that they will force a lot of turnovers. If they keep scoriing 30-40 points and opponents are playing from behind, they might get a decent amount of picks, but that's about it.
But as I keep saying, this team does not have the talent they had before (Law, Samuel, Seymor, Bruschi, Harrison, McGinnest, Vrabel, and on and on). Maybe BB can coach them up and into something much better, but they sure have shown that they are close to becoming elite by any stretch.