I loved Petry in 14-15. There was really no big flaw in his game, and his reliability factor was amazing. 15-16 was the first time he looked to be struggling. Based on the fact he eventually pulled out of the season for surgery, I'm guessing his physical health played a large role in his struggles. Fast forward to 16-17, and I thought he was a mixed bag. Some stretches, he looked awful and in others, he showed flashes of what made me like him so much when he first arrived in Montreal.
Based on his historic inconsistencies with this club, I have no idea what to expect from petry now, but the habs need him to be at his best more than any other season. If that happens, then the defense instantly improves by a considerable margin.... That's how important he is and how much of an impact he can have.