Depending on which side of the fence you stand on, Mayfield's contract is a massive minus for loads of people. Social media was full of negative reactions following the announcement of an extension on July 1 regarding its length. Lou Lamoriello, now 80 years old, likely won't be with the organization come the conclusion of Mayfield's deal, possibly playing a factor into why he was willing to go so long. It was perceived Mayfield would receive an offer from another organization over $4M and perhaps nearing $5M. Where other teams weren't willing to go long-term, Lamoriello closed the deal with fewer dollars over a more prolonged period.
While he's one of the bigger, stronger defensemen in the league, Mayfield isn't the most fleet of foot. His style of play doesn't require much straight-line speed, but he's not too effective using his edges either. As dominant skaters have taken over the NHL, smaller, quicker defensemen have become more and more prominent in the game. The Isles' early season game last year at home against the NJ Devils was an example of this, as the Devils forwards skated circles around Mayfield (and essentially the entire team).
Where he lacks in skating, Mayfield makes up for in physicality, clearing the crease, and giving his goaltenders clear sight of the puck. He may not be a mesmerizing player on the ice, but he understands his role and has become an intrugal part of this team.