Watched this dude's interview on bb.com, love that he is quiet and reserved on camera, almost the opposite of the "im so excited Marrone" (not that Marrone's enthuiasm is bad, Pettine just seems to belay an authoritative confidence is all) and IMO that should help with the teaching of the new stuff he will bring.
There can be no doubt the D is ready for something new and didnt believe in Pornstache's approach. However, I think a guy who would come in and overcompensate with rah rah Gregg stuff might be tuned out. Pettine brings results, but based on how he projects himself in the few interviews and on the field footage i have seen so far, it feels like he coaches in a way that highlights confidence in who he has, not bravado about what his schemes can do or have done.
We'll see. I might be in left field. However, my feeling is he is going to have this D believing in themselves and each other. A middle of the pack (top 15?) improvement may be within reach!