What is the best way of playing it? Classic R* 3rd person with semi-auto aim, or first person manual aim?
I am enjoying the latter in GTAV*, but somehow I feel the classic 3rd person provides a lot additional detail and that's how it is meant to be played.
The correct (albeit somewhat trite) answer is IMO "Whichever way you enjoy it most."

*Stunning how great that game still is by today's standards.
Agreed. I'm not one of those clamouring for GTA VI, because GTA V was so far ahead of its time (and still is) that there's no need.