Perhaps the biggest difference between the New York City of 40 years ago and that of today is the degree to which the major tourist areas have been "cleaned up." This is especially the case with areas such as Times Square.
In the 1970s, Times Square was a pretty squalid place. It was best known for such things as the "peep shows" where people could view pornography in little booths. It was one of the worst areas in the city because of all the pornography, strip clubs and prostitution.
By contrast, Times Square today is "Disneyfied." It is a place for wholesome family entertainment, not the sort of place that families would try to avoid.
This change is symbolic of a more general change in the city -- one in which the city has been made more "livable" in many people's minds by a crackdown on petty crime and vice.