There are some quarterbacks in the league that just plain stump defensive coordinators. If you blitz, they burn you. If you sit in coverage, they patiently dissect your secondary.
So how do you frustrate them? Your team has to have the best of both worlds. Your defense has to have good corners capable of playing press coverage and zone at any given moment. However, the most critical component is a very capable front four. If your defense can get pressure on the quarterback without having to blitz, you've already won a battle.
By not having to blitz, you open your linebackers and corners to being able to play zone or man instead of constant man coverage. Of course, the quarterback is still going to get his, but he's going to have to work harder to get it.
So what does New York have? Everyone knows about the Giants' front four. It's the same front four that harassed Brady in 2007. This defense has given up the 11th-fewest passing yards in the league, but has given up the sixth-most rushing yards in the league. This is a day that Brady needs to let the Patriots running game go wild as he's likely to end up struggling against this defense.
However, a bigger worry for the Patriots is the Giants' offense. Quite frankly, any team with a passing offense will give the Patriots fits. Their defense, specifically the passing defense, is pathetic.
So while Brady is struggling to put points on the board and having to let his run game slowly work at the Giants, the New York will be able to pass at will.
This is going to be frustrating for the Patriots and their fans to watch. This doesn't mean the Giants will win, but it's going to be a frustrating win at best for the Pats today.