To start: (IMO)
1. Less outside shooting today than during Issel's day, especially mid-range shooting.
2. In the same vein, the dunk has taken over. Obviously that requires less skill than size.
3. Today's players are allowed to do things with the ball that would have resulted in a turnover in Issel's day. During the play-offs, on multiple occasions, I saw LeBron get the ball in back-court and take a couple of steps before he decided to dribble. Camping under the basket; carrying the ball, etc... That crap would not have been allowed.
4. The game is much more physical now. Too much grabbing, pushing, shoving, etc... In Issel's day, fouls were called for that type play. ****And this is the problem with today's officiating. There is no longer a definite standard governing physical play, thus lots of inconsistency relative to officiating.
Today's players are better athletes, but they don't have the basketball skills players had in Issel's day. On the other hand, a player like Dan Issel would be just as successful in the nba today as he was when he played. He'd adapt.