Way more athleticism involved in todays game. Most notable is the LB position. The days of the big burly run stopping Middle LB are long gone. Those dudes gotta run and be able to cover in space now. It feels like the safety position players of the 80's are now playing LB in todays ball.
It's been brutal at times. The quality and complexity/creativity involved in the game in the 60s and 70s and somewhat in the 80s was quite poor. But, I enjoy getting a deeper perspective and understanding of what the game was like back then than you can get just from reading old newspaper articles or watching 30 for 30 type of shows. And of course there are some aspects of the sport that were better then. Much more passion and commitment to the team; no instant replay fouling up authentic reactions to the outcome of plays for example.