The NFL's new Overtime Rule states that if the team that wins the coin toss scores a touchdown than the game is over whereas if they kick a field goal the other team gets a chance to make or break that. This rule is in effect for postseason games only.
Why not include the regular season games? You can't get into the postseason unless you win in the regular season. The games in the regular season have an impact on what happens in the postseason and the same overtime rules are in place for those games still. There's games in Week 17 and other weeks of the NFL that could have an effect on playoff berths, and who makes it and who doesn't. Suddenly if you get to the playoffs and have to go to overtime you experience with something you haven't experiment with before and have no prior experience doing.
For the regular season and the majority of the games the same crappy overtime rule applies so it doesn't change anything at all there.
Now within the rule itself, one thing that did not fix is that the team that loses the coin toss still may not get a chance to score in overtime. Say there's a huge play that goes for a touchdown, the other team that lost the coin toss never get's a chance to get the ball. That's basically the same thing as the old overtime rule just without field goals which doesn't do much.
The NFL solved some aspects of the problem but far from fixed it. It's as if they had a dirty table and decided to clean only 1/4 of the table instead of the full table.