Maybe I'm reading this wrong, or perhaps I just never played right in 3.5, but I seem to remember this idea of "threatened squares" which appears done away with in 5e.
A mighty warrior approaches a giant wielding a club. The giant has a reach of 10 feet. The warrior gets within 10 feet of the giant (newly within range) then moves one more square, now 5 feet away, in order to make it's own attack.
In 3.5 the warrior moved through a threatened square, provoking an attack of opportunity.
In 5e the warrior did not move out of reach (only into reach), thus did not provoke an opportunity attack.
Do I have a proper understanding of how this same scenario is effectively different given the new versions of the game?