MacKinnon definitely turns it up a notch in the playoffs, although you'll still see similar play from him throughout the regular season. We get a little too caught up in pucks going in and assists being tallied rather than just absorbing the play on the ice. I have more fun watching MacKinnon than anybody else. He has a different kind of aggression that you just don't see.
I feel like McDavid goes completely missing in the playoffs in a couple of games every series. Maybe it's just me, but my takeaway from McDavid never reaching the finals (besides awful goaltending) is his lack of intensity come playoff time. You never really see him turn it up a notch, but maybe he's just always consistently playing to his full potential.