Where to begin...I'll take the first 3 that come to mind.
1) Mario is miscast as part of the big 4, his offense was elite but his ESGF/ESGA shows that his impact wasn't nearly as great as the legend about him.
2) Playoff seeding should be 1-16, 2-15, 3-14 ect.. to even out travel for all teams and promote the idea that the 2 best teams in the NHL can actually come from the same conference.
3) Install the floating blueline like in ball hockey.
When a team gains the blueline, the line for offsides floats back to the center red line (which in essence become the blue line) thus providing more time and space for the skill in hockey to shine through.
I lied there will be a fourth one
4) Reduce the size of the goalie equipment more in line with historical sizes while keeping safety. The equipment still is too large and is there to prevent goals more than preventing injuries.
Heck I'll even add a 5th one
5) All goals should count, other than high stick ones, if a player kicks it in it should still count, heck he can even direct it in with his hand if he wants but still no closing the hand around the puck.