The New Jersey Devils defense is still the major flaw of the team, despite how much better it got in a calendar year. Adding Will Butcher and Mirco Mueller before the year gave them one really good top-four guy and a decent depth piece. Ben Lovejoy found a much better role, and was actually a plus player for much of the season. By far the biggest piece of the puzzle was trading for Sami Vatanen.
It took him a little over a month to hit his stride, but once the calendar changed to 2018 he was the number one guy.