While so many make the point that Brady's been in the same offensive system for 20 years, that is FAR from the truth.
The only thing that remains the same is the basic language used, and even that has evolved over the years (as all languages do). Brady's played in MANY different offenses over the year. What makes the the Pats system so effective that it can evolve into what is needed to match the talent the Pats happen to have that year, and to effectively compete against the changing defensive alignments and personnel changes that have occurred.
HOWEVER the price of all that flexibility is the complexity and long learning curve, especially from the skill positions. Often it takes an entire season to become fully acclimated. Same goes for the defense. That is why rookies often "participate" their rookie years, but don't fully "contribute" in a meaningful ways
That being said, I think Williams, Winovich, and Cowart are going to be a BIT more than participants this season. But it looks like we whiffed on the offensive side so far. Go Gunner.