The decline in run-blocking seems pretty easy to diagnose. The Pats replaced Neal with Waters, whoase run-blocking abilities had been in decline for a couple seasons (according to knowledgeable KC fans). They also lost underrated run-blocker Koppen early and replaced him with Connolly. Connolly's run-blocking at guard had been pretty good, but the requirements at center are, of course, somewhat different. He did improve over the course of the season, though (IMHO) he never quite made it to Koppen's level, and his improvement was delayed by injury, during which time the subs, Wendell and McDonald were relatively poor even compared to Connolly.
I still maintain, though, that a significant piece of the Pats inability to run effectively was the limited abilities of the primary RBs - BGE and Woody. BGE works almost exclusively between the tackles and is rarely successful going outside (and doesn't run a lot of pass routes). Woody can get outside and can run quite a few routes, but isn't consistently successful between the tackles. So defenses can play the odds (even out of their nickel) as to what kind of running play is coming based on which RB is lined up in the backfield. Sure, sometimes they get burned with a BGE run to the outside (or catching a pass), or with Woody running between the guards, but there's no real lasting effect for the offense. It certainly seems to make play-action somewhat less effective.
This, of course, is where Ridley comes in (and, we hope, Vereen). Ridley appears to offer about 80%-90% of what both BGE and Woody can do - meaning that defenses shouldn't be able to key in on RB tendencies (at least, not as readily). So, assuming Ridley can correct his insecure ball-carrying habits, he should be able to improve the ground game which, in turn, should have a positive impact on play-action effectiveness, which, in turn, could make life a little easier for outside/deep passing targets.
