Hard for me to judge for you Blastman, but for me? Los Santos is one the most convincing game worlds I've ever seen. Single player is very alive, with pedestrians, traffic, aircraft, animals and more. That said, it is a 2013 game at it's core.

Online reduces the NPCs to a certain extent. less traffic for example (which is nice for street racing!)

But yeah, GTA really blew me away with the world, and I didn't start playing until it was a few years old. I still love it hundreds of hours later. NPCS will walk by having conversations on their phones (walk along and listen it's often a hoot), they will get defensive if you get too close or bump them. They might place a bounty on you for nicking their car. Everywhere you turn it's populated. Not sure where your standards fall, and GTA may not meet them, but for me I reckon it's one of the best.