Lemieux, 2001. I've refrained from voting for it until now due to games played - but I think it's time. Yes it's only 43 games - but it's an absolutely ridiculous comeback, at age 35, to play at such a high level, after being away for so long.
He led the league in Points per game, Assists per game, and Goals per game.
His points per game was 1.767 - No one since 2001 has posted a higher ppg. The last player to post such a high one was Lemieux himself, in 1996 (Jagr also that season). Right smack in the middle of the dead puck era.
His goals per game of 0.814. Also the highest of any season since 2001, and the last player to post a higher GPG was Lemieux himself, again in 1996. (Bure did come close the season prior, with 0.784. Ovechkin's highest GPG is 0.793 in 2008).
His assists per game was 0.954. Also - best in the league. That number isn't quite as historic as the first two, but still, it's the highest total of any player in a 3 year period.