Just a few things, like enforcing obstruction rules. They've changed how you can pass the puck (you may now pass it over two lines), they've changed how the goalies are allowed to touch the puck behind the goal line... Also, ties are now taken care of by a 5 minute overtime period, followed by a shootout.

The problem is that there are a MILLION penalty calls per game, now, as players struggle to adjust to the new reality of an obstruction-free NHL. People say it upsets the flow of the game, and it does, but teams are starting to adjust and the game is flowing better when it's being played. :) Hopefully, the officials will continue to call the penalties by November -- usually they give up in mid-October.